In June, with so little fanfare they weren’t even listed on the bill, Roger McGuinn and Chris Hillman took the stage at Nashville’s Ryman Auditorium to play a song from “Sweetheart of the Rodeo.”

They last did that on March 16, 1968, and it did not go well. They were the Byrds then, and the appearance at the Grand Ole Opry elicited boos, catcalls or indifference, depending on who’s telling the story. This time, backed by Marty Stuart and his band, the Fabulous Superlatives, the crowd cheered as McGuinn and Hillman kicked into “You Ain’t Goin’ Nowhere,” the Bob Dylan song that opens “Sweetheart.”

“I cried,” says Tyler Mahan Coe, a country music historian who hosts the popular “Cocaine & Rhinestones” podcast. “I never even imagined that it would hit me as hard as it did.”

It’s fitting that Coe was born 16 years after “Sweetheart’s” original release. Back then, the album stiffed, sparking the end of one of pop’s great partnerships. But over time, that sixth Byrds record has climbed from bargain bins onto most-important-ever lists. And now, at 50, “Sweetheart” is recognized for inspiring musicians from the Eagles and Elvis Costello to next- generation alt-country players such as Ryan Adams and Wilco.

“The template,” says Jay Farrar, who founded Uncle Tupelo in the 1980s with Jeff Tweedy before forming Son Volt.

“Every generation has this new take on roots and back to basics,” declares Scott Avett of the Avett Brothers. “Sweetheart of the Rodeo” is one of those great milestones or benchmarks.”

This year, Byrds founder McGuinn, 76, who regularly turns down millions to reunite the Byrds, recruited Hillman, 73, to celebrate the album with a short tour. They started in California last month and will continue in September with gigs in, among other spots, New York, Boston and Virginia.

It’s not a Byrds reunion, particularly with the third living founding member, David Crosby, not involved. But the set list isn’t limited to “Sweetheart.” McGuinn and Hillman explain how they got to Nashville by digging deeply into the Byrds catalogue, with hits such as “Mr. Tambourine Man” and “Turn! Turn! Turn!” melding with lesser-known tracks that show how country music influenced them.

“Sweetheart” wasn’t just country-tinged. It was driven by banjos, fiddles and pedal steel guitar. It also launched Gram Parsons, who would quit the Byrds after a single record to embark on his short, influential career.

From L.A. to Nashville

They were called the Jet Set when CBS signed them in November 1964, but quickly switched to the Byrds. By April 1965, they released what became their first No. 1 hit, an electrified take on Bob Dylan’s “Mr. Tambourine Man.”

The Byrds were defined by McGuinn’s 12-string Rickenbacker 360, with its thick, jangly melody lines, as well as the gorgeous harmonies of McGuinn, Gene Clark and David Crosby. Hillman, a Los Angeles native with a passion for bluegrass, had joined to play bass. In early 1967, the Byrds released his collaboration with McGuinn, “So You Want to Be a Rock ‘n’ Roll Star.” The Byrds would have three more Top-40 hits over the next year before tensions led to Clark and Crosby’s exits. “The Notorious Byrd Brothers,” an innovative, psychedelic pop record released in early 1968, was largely created by McGuinn, Hillman and session players.

Then, while standing in line at a bank in Beverly Hills, Hillman ran into a sandy-haired kid from Georgia who said he could play piano. Hillman brought him to McGuinn. Parsons was just 21.

“I asked Gram if he could play some McCoy Tyner type of piano,” McGuinn says. “Because I was into John Coltrane and the “Eight Miles High” kind of place. And he played some Floyd Cramer-style piano. Floyd played on Elvis Presley’s “Heartbreak Hotel.” That was a song that got me interested in music. I thought, ‘Wow, this guy’s got talent.’ But I didn’t know he would turn into George Jones in a sequin suit.”

Parsons didn’t hide his true love. At the end of their first rehearsal, Hillman remembers Parsons kicking into a Buck Owens song. The Byrds were trying to figure out their next step, with McGuinn talking up a sprawling, conceptual album with a futuristic suite. Parsons had his own idea.

“He was totally enamored with country music, and he was great,” Hillman says. “Personable, energetic — he was everything we needed right then and there. After a night or two, we finally hired him. Then, we discussed the album. Of course, Gram was very ambitious, and Roger and I were spinning our wheels at the time, but had been around the block a few times, and it was nice to have that energy. He was really pushing for the country, which was fine with me.”

Dylan had gone to Nashville in 1966 to record “Blonde on Blonde.” “Sweetheart” wasn’t about merely a geographic shift from California to Tennessee. It also wasn’t, as many would write, the album that invented country rock.

“Country and rock were blended decades earlier,” Coe says. “Rockabilly is rock and country music. That being said, ‘Sweetheart of the Rodeo’ is hugely important, because that is a band that had achieved success as a rock band or a pop band even, pivoting to country.”

They were also doing that pivot when fans of rock and country were on different sides of a cultural war. This was the height of Vietnam, the Acid Tests and Richard Nixon.

The Byrds did not go to Music City to push free love. They went there to do a country album and to record songs made famous by the Louvin Brothers and Merle Haggard. They hired the greatest “Nashville cats” to back them. They chopped off their hair, and McGuinn left his mini-rectangular shades and his Moog synthesizer back home. But the atmosphere in the studio felt different from country sessions. Pedal steel player Lloyd Green showed up at Columbia’s Studio A on Saturday morning, March 9.

“I was used to a routine where we did four songs every three hours,” Green says. “We had 45 minutes per song on a recording session, whether it was Dolly Parton or Charley Pride, and these guys, they weren’t looking at the clock. They would just sit around and talk a while. Finally somebody, probably Gram, said, ‘Let’s play a little bit of this song.’ The first song they started playing was the Dylan song. “You Ain’t Goin’ Nowhere.” I said, ‘Where do you guys want me to fill?’ They said, ‘everywhere.’ ”

'Our kind of music'

There is a legend that surrounds Gram Parsons, one that’s only partially about the heartachingly beautiful songs he produced. The mythology developed from the dreamy eyes and Nudie suits, the hanging out with Keith and the “Wild Horses”-era Rolling Stones and, of course, what happened after his overdose Sept. 19, 1973. Manager Phil Kaufman stole Parsons’s body from a loading dock at the airport and, as the sun rose in the Mojave Desert, set it afire, according to the singer’s wishes.

All of that came later. The Gram of 1968 was very different.

“Wonderful, sincere, sweet, sensitive, not just great as an artist but what a wonderful kid,” says pianist Barry Goldberg, who played with Parsons on “Sweetheart” and backed Dylan’s electrified Newport Folk Festival set in 1965. “Some guys come in and think they’re the deal. Gram had none of that.”

In the past, Parsons has been described as trying to take over the Byrds during the “Sweetheart” sessions. It’s an idea McGuinn brushes off today.

“Gram and I got along,” he says. “He was so into the country sound that he didn’t feel the Rickenbacker would blend well with a steel guitar, so he mentioned replacing my guitar and maybe me too, but it wasn’t a serious problem or negotiable.”

There was one choice that led to a debate that continues today. Producer Gary Usher had McGuinn and Parsons record lead vocals for many of the same songs. But when “Sweetheart” came out, McGuinn’s leads dominated. One argument is that McGuinn did this to assert himself, and this angered Parsons. Others point to record label head Lee Hazelwood’s threats to sue Parsons, who had signed a deal with him before joining the Byrds. The 2003 expanded reissue of “Sweetheart” added all of Parsons’s vocal takes.

McGuinn concedes that Parsons sang at least one of those songs better than he did during the original sessions. McGuinn overdid the Louvins’ “The Christian Life” with an exaggerated country accent.

“I was doing almost a satire on it,” he says. “I was not a Christian at the time. Back then, it was kind of tongue in cheek. I know the Louvin Brothers meant it when they wrote it and sang it. And Gram meant it. He was a little Baptist boy.”

While still making “Sweetheart,” the Byrds were offered a glimpse of how hard it would be to reach a country audience, even if they had the best intentions.

That March, while in Nashville, somebody suggested the Byrds play the Grand Ole Opry. The Saturday night radio show was, for most country singers, the ultimate gig, a chance to perform on the same hallowed stage once occupied by Hank Williams, Patsy Cline and George Jones. A Columbia staffer secured a slot for the Byrds on March 16.

Green agreed to play the gig. Looking back, he understands why the booing began before they had even sung a note.

“There was a them-and-us thing, and redneck America and the younger generation for sure,” session musician Lloyd Green says. “They sang the song while the audience was booing.”

There was also a game-time decision by Parsons to follow the Dylan opener with his own “Hickory Wind” instead of the scheduled Merle Haggard song, “Sing Me Back Home.” This infuriated Tompall Glaser, who had already announced the Haggard song. He screamed at the Byrds when they came offstage.

Later that week, McGuinn and Parsons headed over to see popular Nashville DJ Ralph Emery. The first thing Green remembers is Emery scolding the pair for coming to Nashville to do “our kind of music.”

“They were speechless,” Green says. “They didn’t know what to say. Then, when they were fumbling for words, he turned to me and said, ‘and you, Lloyd, why would you give your talents to this?’ ”

Bargain bin to gateway record

In 1985, McGuinn went on the TV show “Nashville Now” to back Vern Gosdin’s performance of “Turn! Turn! Turn!” He then sat down for an interview. The host was Ralph Emery.

“Roger, have we met?” Emery asked him.

By now, McGuinn had become a Christian. He spoke softly and responded to most everything with a warm smile. He had short hair and wore a tie and sport jacket.

“Yes, we have, Ralph,” McGuinn said, without a hint of nastiness.

He reminded Emery of the time he brought him a record to play.

“But I didn’t play rock groups,” Emery said.

McGuinn, still polite, admitted he had been hurt by the rejection.

“You didn’t understand where we were coming from,” he said. “We had fallen in love with country music in 1968. . . . We went ahead with ‘Sweetheart of the Rodeo,’ we were trying to do a real, sincere country album. We were really sincere at that time.”

The fact that “Sweetheart” bombed still disappoints McGuinn.

“Nobody liked it,” McGuinn says. “I was very surprised it didn’t go over well. It just sounded great.”

In the aftermath of “Sweetheart,” Parsons quit and Hillman joined him to form the Flying Burrito Brothers. McGuinn, in turn, reinvented the Byrds by adding guitarist Clarence White, a regular sideman for the band. White, a masterful player, helped invent a piece of hardware that allowed him to bend the B string of his Telecaster to almost replicate the sound of a steel guitar. He called it a “B-Bender.”

And “Sweetheart” developed a second life.

Gillian Welch, now an alt-country icon, was in college in the late ’80s when she picked up a used copy at Logos, a record store in Santa Cruz.

“It was my gateway record,” she says. “It’s like the spokes of a wheel and, in many respects, my record collection radiates out from this record.”

Marty Stuart was just 13 in 1972 when he moved to Nashville to play in aging bluegrass star Lester Flatt’s band. Around that time, Stuart found a copy of “Sweetheart” in a bargain bin at a mall.

He loved the record, loved the Byrds, but was struck by the wall between the old-time country players and the younger musicians who admired them. He witnessed it firsthand when he backed Flatt on a Michigan State University bill in 1973 that also featured Parsons, Emmylou Harris and the Eagles.

“They were all excited about meeting Lester Flatt, but I found it really interesting that Lester didn’t know who any of those people were,” Stuart says.

By the end of 1973, Parsons had died, at just 26, of the overdose. White would also be gone, killed that same year by a drunk driver. In 1980, Stuart bought White’s B-Bender Telecaster from his widow for $1,450. You can see him playing it, for the first time, while backing Johnny Cash on “Saturday Night Live” in 1982. It remains his regular guitar.

McGuinn met Stuart for the first time in the late 1990s. Stuart showed the singer how he had learned all of White’s “Sweetheart” licks. He also apologized for what had happened at the Opry, even though he was 10 years old at the time.

“Give me another chance at that,” Stuart said, inviting McGuinn to play with him.

That led to a show at the Opry in 2010.

“And man,” Stuart says, “from the minute he walked in, it was like a prince had returned. He was honored and loved.”

That same feeling pervaded the Theatre at Ace Hotel in Los Angeles last month, as McGuinn and Hillman — backed by Stuart and the Fabulous Superlatives — opened their “Sweetheart” tour.

In the lobby, a woman with the album’s logo tattooed on her back caught the eye of Craig Butler, the artist who adapted Jo Mora’s rodeo poster for the original cover. Dwight Yoakam, with his cowboy hat, took a seat in the orchestra section. So did Mike Campbell, the longtime guitarist in Tom Petty’s Heartbreakers. The late Petty, a huge Byrds fan, produced solo records by both McGuinn and Hillman.

The concert opened with the Dylan-penned Byrds staple “My Back Pages” and Hillman’s vocal on the country-influenced, pre-“Sweetheart” song, “Time Between.”

Finally, after a short break, Stuart returned for the second set and proclaimed, “Can you believe what we’re going to experience?”

McGuinn sang “You Ain’t Goin’ Nowhere,” Hillman took “Hickory Wind,” and Chris Scruggs, grandson of the legendary banjo player Earl, put down his bass for the pedal steel. McGuinn got his do-over at “The Christian Life.”

“I didn’t really know what it meant,” he told the crowd. “I do now.”

After that first concert was over, McGuinn, in a phone call, talked of how much he loved performing those songs again, looking over at Hillman, and also about how moved he was by Stuart’s playing. “Listening to Marty play his Telecaster with the B-Bender, it was like being with Clarence White again.”

But he didn’t make too much of the crowd’s cheers. They felt good, sure, but “I’m not really into vindication.”

“It was just a great show.”

An earlier version of this story used the name Nelson for Lloyd Green.