quick question for the group. To switch from SBP to BBP, I need to change the shafts, drums and backing plates? brake internals the same or all of that too?
yes.
LOL
Seriously you can skin that cat a few different ways.
The factory '68 Hemi A-bodies came used a limited production front rotor and hub, and a redrilled or special rear axle with the large bolt pattern 10 x 1.75" drums from /6 B-body cars of that year.
At the other end is swapping in late model A-body front disk brakes and 8.25" rear axle which IIRC has the 10 x 2 and something drums