What A-body did this 8 1/4 come out of?

66fs said
Just sent an axle housing to Moser to be shortened. BBP axles are longer after the bearing, so the housing needs to be shorter to keep the same track width. Uses standard BBP wheels and backspace which keeps the wheels centered in the wheelwell, without thinking.

You're right about the axle stand off being different for the BBP axles, they are longer and switching to BBP axles (and brakes) from SBP axles does increase the track width, usually about 5/8" to 11/16" total, or ~5/16" per side.

But, the 51.5" flange to flange measurement doesn't keep the track width the same between the SBP 8 3/4" and the BBP 7.25 (or 8.25, apparently). The drum to drum measurement on the SBP A-body 8 3/4 is 57-1/8", the BBP 7.25" is ~56-5/8" drum to drum.

That still works out to a difference of 1/2", which doesn't sound like much, but it does change the backspacing a 1/4" if you want to keep the wheels in the same place. Not usually a big deal if you're running stock size tires/rims, but if you're going big that 1/4" is more than enough to cause interference.

The difference is even worse if you're moving from an A-body BBP 7.25 or 8.25 to an A-body 8 3/4 with BBP axles and brakes, that difference is 1.125", or 9/16" per side.