In one of the Fiero Anniversary threads on PFF, it was mentioned that the 89/90 prototype on display isn't really roadworth enough to hold up for much driving. Some of the undercarriage was cobbled together and wouldn't have been the final production manner. An individual took as many pictures around, in, and under the car as possible, because someone questioned if a kit couldn't be made to resemble it.
I have a file on the prototypes, including the notchbacks. They resembled the Buick Reatta. I met a guy at a Canton car show who was displaying a Reatta and he felt that some of it's lines were pulled from the Fiero prototype notchback.
It's common knowledge that the Fiero GT lines were used in the later Camaro and Firebirds.