guys here are using B body rears so they can use the 17" mustang rims with 5.72 backspace without having to use spacers. the 5.72" bs wheel fits in the wheel well dead nuts centered, so a 5.50" bs wheel would likely fit very nicely.
I don't know anything about using 17" Mustang rims, but I always liked using B-body rears in Dart Sports and Dusters because you can get them a lot cheaper than an A-body 8 3/4. I was able to shove 10" wide rims w/ 6.5" backspacing just by installing the 3/4" spring relocation kit. No tubbing required.
