This is correct. It all depends on what axles you buy for your bbp conversion.
I ordered axles from Moser, and they asked if I wanted bbp offset, or sbp offset.
I got the sbp offset axles, then used my existing brakes, and just redrilled the larger pattern on my drums myself. Its not difficult. And as far a the size of the centering hole on the axles/drums, the center hole on my sbp drums was an exact fit to the center bump on the new axles.
To mark for the new holes, I just set the drums on the new axles and marked through the lug holes on the axle. (the studs werent installed yet). Just remember when you drill the drums, the studs are 1/2", but the knurled part of the stud sticks out of the axle enough to engage the lug holes in the drum. So you have to have a drill bit thats just a little bigger than 1/2"
Good luck