I have a 9" rear. It measures 53 1/2" from the face of the axle to the face of the axle. I'm thinking this is about 3" shorter than a factory rear as what I've found online says a factory rear is 56 1/2". With stock wheel wells what is the width of you guys rear and what rear wheels are you running? I'd like to run a 7" or 8" wheel, but I'm thinking my rear might be to narrow as I'd end up needing 2-2 1/2" backspacing.
53-1/2 would mean the axles would be 5-1/4" away from the center of the springs if I'm remembering correctly. My memory is a bit fuzzy but I think the 9" I used was 53" from flange to flange on the housing. I'm running 10" wheels with a 5" backspace.