Why do you need 17x9.5"s all the way around? I was under the impression that the 4th gen F-Body would support up to 11" wheels in back with no mods? I know I managed to stuff 17x11"s in my '87 IROC with minimal modifications (ok, if you call pushing the quarter panels out 3/4" with a portapower "minimal" - but it didn't take too long).
Also, if you're going to run any sort of power behind it or are running an A4, you'll definitely want the wider wheels. My IROC would spin the 275ZR45-17s every time it shifted - that went away with the 315s.