a body rearend question

I doubt your B-body axles can be shortened and re-splined to a-body dimensions. I used to have a list of eligible donor cars and I believe for B-bodies, only a very few years of wagons in the early 70's had enough length.

The typical donor cars are 70's C-bodies and vans and pickup trucks from that era. There is an easy dimension check you can do with a tape measure from the outside surface of the flange to the point where the axle starts to taper to see if it's long enough. But it's been too long and I don't remember the magic number. I took pictures with a tape measure of the before and after shortened axles but I don't have access to them here at work.

I used C-body axles (used for $35/pr) and sent them off to Moser for shortening/re-splining. It was about $100 at the time. Don't quote me but I think the shortened axles were exactly 29" when finished. This was probably 6-7 yrs ago and Moser turned them around in no time, 3-4 days including transit time.

But wait...there's more. You need to get new backing plates, hardware, drums, and shoes that are compatible. There is an offset built into the backing plates that only work with the matching parts. If you have brakes on your b-body axle, that would be a nice matching set. Then you need wheels to match the BBP. I pieced all my junk together from swap meets and Rockauto over a period of a year or so.

I distinctly remember checking before and after measurements using a plumb bob to the floor and the conversion added exactly 3/8" to each side for a total track width increase of 3/4".