Well for mine the back spacing is 6.0" on a 9.5" Just remember that my car is NOT stock and I'd hate for you to use those numbers a have a problem. I bought a very cool tool thats kinda expensive but when your wheels fit perfect it's worth it. Percy's back space tool.
http://store.summitracing.com/partdetail.asp?autofilter=1&part=PHP%2D01201&N=700+115&autoview=sku Its 89 bucks at Summit I actually got mine from Speedway. It works great and takes the guess work out. The bummer is when you see it you think A. I could make one of these. B. It should cost $19.95! All well If you plan on building more then one custom car in your life it's worth it. The rears are a 8" backspace on a 12" rim with a stock width rear end and a lot of wheel well massaging.
I'm debating if I should go air or coil-overs
Exvelocity I saw the heat you got on your other post this is for you! Maybe I'll post it over there also and stir up the pot!
On the Air Ride I rode in a mustang with the new shockwavs and thought the ride was nicer then expected it's smooth more like a new car but not by any means soft. It was a short ride so I cant say about every road surface but I was impressed enough to go with it. Not at all bouncy like an older bagged hot rod with external shocks. Read this it helped me
http://ridetech.com/streetchallenge/streetchallenge2006.asp I've heard all the arguments about stock vs modified coil vs bags. I like torsion bars I have a stock Challenger 383 4speed. I have a heavily upgraded factory system in my Challenger Convertible. My first and foremost goal was to make Twisted Fish ride and drive like a new car. Smooth riding and great handling. crisp steering and no bump steer. Theres a number of things a new car uses to achieve this. A stiffer body softer springs. and better geometry. Add to that rack and pinion steering. and multi link read suspension. You can't duplicate that with out a lot of modifications.
In answer to you question I hope I have a smoother ride then stock that will out corner it and hook up better.
The icing on the cake is being able to adjust the ride hight on the fly! I got to be LOW
The rest I'll let you know when I finaly get to drive it.