After talking to Cass at Dr. Diff, I have a plan...
Going to put the rear wheels and tires under the car with no rear end and space them where they look/fit best with the leaf springs back on so I can see clearance.
Measure the distance from wheel mounting surface to mounting surfaces and work the math to figure out what width the rear needs to be flange to flange.
Maybe the B body rear will work as is. If not I will,
1) Shorten the housing and order custom axles from Dr. Diff.
or
2) Order a complete A-Body 8-3/4 housing and custom axles from Dr. Diff.
Regardless I will pay a little extra for custom axles to fit my Jeep Cherokee rear disc brake setup with whichever rear housing I end up with.