Guys, thanks for the help!
Joe especially, those measurements are exactly what I was looking for. I have scrounged up a lot of cardboard and plan on using that to make up some dummy bedsides and fenders. I'm going to be using the rearend out of a '55-'56 chevy sedan, which I think is 2" narrower than the Trans Am rearend, and I also plan on using the 2" wider fenders, so I should be able to get some good sized sneakers out back. Oh, and I would use the running boards, but those are gone too! Again, thanks for spending your hard earned time to help me out, I really appreciate it.
Eric