I'm up in Canada and remember seeing an ad in an old Auto Trader of a company that made fiberglass bodies of a '55 or '57 chev convertible that either mounted on a stock frame, or you could use a'77 to 89 full size Impala or Caprice frame. Being the pack rat that I am, I dug around and found on old copy(2002). The name of the place is Prototype Research and Development , 230 Albert Lane, box 1330, Campbellford, Ont, Can. KOL 1LO.
97050 653-4525. They might have an email address, I don't know. Hope this helps. Good luck.