General Motors' Cadillac division signed a $100-million agreement with Alitalia and Lufthansa to fly Italian-made car bodies from Turin, Italy, to Detroit for the 1987 model Allante roadster. Cadillac said the contract calls for the Italian and German airlines to transport 56 car bodies on specially outfitted Boeing 747 jumbo jets three times a week. The exterior bodies for Cadillac's two-seater sports coupe, to be designed and built by Pininfarina, the Italian car design firm, will then be attached to their chassis at GM's Poletown assembly plant in Detroit. The flights will begin in October, 1986. GM plans to build about 7,000 Allantes a year.