i know there has been talk about updating the rear suspension with the corvette C5/C6 rear suspension as this company https://rick486.wixsite.com/dobbertinperformance makes a kit to put it in other cars but i feel all that needs to be known is where to put the upper mounts for the upper A arm and from what i can tell the corvette cradle needs just about 3.5 inches of narrowing

It was done way back in 2005. Start on page 25 and keep going for about 10 pages. It starts with tubular cradle and C5 bits cut into the stock frame rails, but ends up with new rails and the stock lower C5 cradle.
https://www.fiero.nl/forum/F.../HTML/000007-25.html

Vince & Mike are working on front/rear C5 setup for Vince's car:
https://www.fiero.nl/forum/F.../HTML/000142-13.html

thanks