So I confirmed that my shaft measures about 31.375". Combine this with the other shaft and a 0.8" diameter center pin and I have about a 63.5" WMS to WMS measurement. This seems to fall in line with the later (70.5+) shafts.
When you provided the 55" vs 57.5" housing measurements, where are those taken from? Is it the inboard sides of the backing plate flanges or the outboard sides of the backing plate flanges? Or somewhere else entirely?
My brakes shoes are 2" wide, but the drums measure about 4.25" when I lay them flat on the ground. I don't have a good reference for a proper brake drum to brake shoe width comparison, but it does seems the shoes are almost too narrow for the drums.
I'm thinking I might have the setup described in this post:
http://67-72chevytrucks.com/vboard/s...d.php?t=215095