A moment's chatter, now, with Sly Stallone's papa. Frank Stallone roosts in a 200-year-old farmhouse in horsey Potomac, playing polo. But, darlings: Don't ask him about the Rock. He and Sly haven't swapped Word One for a year and a half. They had a ghastly "showdown," midway through shooting "Rocky III." What makes Frank simply furioso is the way Sly natters on about his Roots. (He naughtily tells chums he grew up church-mouse rock-bottom poor in "Monkey Hollow." He really means Montgomery County.) "Those stories are absolutely ridiculous and Sylvester knows better. He's always had the best--the best schools, the best clothes, the best of care," his wounded papa just told Patricia Sagon, the belle of Group W Newsfeed. "I think perhaps he ought to set the record straight and be proud of his past." On top of that, Frank tells Ear that his polo ponies did not cost $200, as slippery Sly told last week's Time mag. "They cost me $1,500 each! And that's 20 years ago!" What's more, Papa's not racing out West waving the olive branch. "I love my son but it's his move to make, not mine . . . He knows where I am. I'm not gonna run to him because he's a big star." Clip Ear and mail to Sly, please. Then read on.