A body BBP axle length for 8 3/4"
If nobody gets to it before me, I can get this measurement for you tomorrow. I have a set of original 8-3/4 axles, SBP that were re-drilled with new studs welded in to make them BBP.
Be aware, if you decide to go aftermarket for a set of new BBP axles, the ones from Dr. Diff are excellent, but they are a bit wider than the stock ones. If you are super-tight on your wheel/tire/backspacing/fender clearance/etc it can rain on your parade. Ask me how I know...