Marriott Corp., the diversified lodging and food-service company, has created two senior positions to manage its restaurant and food-service divisions, which are expanding dramatically as a result of the company's acquisitions this year of Howard Johnson Co. and two food-service firms. Daniel P. Howells, formerly president and chief executive officer of Six Flags Corp., a Chicago-based operator of theme parks, has been named executive vice president in charge of the company's food-service management division. He will have responsibility for all operations and staff functions of the division, which more than doubled earlier this year through the acquisition of Service Systems Corp. and Gladieux Corp. J. Michael Jenkins, recently chairman of S & A Restaurant Corp., a division of Pillsbury Co., has joined Marriott as executive vice president and general manager of the Big Boy Family Restaurant chain. Marriott has said that most of the 350 Howard Johnson restaurants it will acquire when the merger is completed will be converted to the Big Boy chain. In an unrelated development, Marriott has named William J. Shaw senior vice president for finance planning and control. Shaw, previously corporate vice president, will oversee the controller's department, and the areas of tax, risk management and internal audit. And William W. McCarten, formerly group vice president of finance, has been promoted to vice president of finance and corporate controller, with responsibility for corporate accounting, operations planning and control, international finance and management consulting.