I do not know the complete and detailed history of the Ford Utica Trim Plant. I do know they assembled the convertible tops to the frames. I remember seeing a photo of the buck that held the top frame while the material was being installed. I do not believe they manufactured vinyls of any kind there. Convertible top material was and still is from Haartz. I believe they currently supply 98% of the world market for convertible top material. Utica was more a of sub-assembly point for seats, top frames, visors, etc.
There is good info on Wikipedia on the Packard Proving Grounds. Went to many a car show there. When the track was still drivable every car entered into the show got a lap around the track. Fun times.