Although this wont answer your question, but I too am using Fiero seats in a 32' 5W. The Minivan seat sounds like a good idea, as I have a 2000 Voyager, and the "2 seater" middle seat seems like it would work good.

Its a shame I wasnt aware of this site awhile back, as we sold the original bench seat, and the flathead engine...or should I say basically "gave" them away.

Good luck,
Greg