8 3/4 rear sbp to bbp help needed plz

There are 2 basic ways to do it:
1) take original axles and drums to a machine shop and have them re-drilled to desired bolt pattern. Studs end up near outer edge of axle flange but works well for moderate HP applications and maintains stock rear brakes/hardware.
2) Buy aftermarket axles or have C-body or truck axles cut and resplined to proper length then convert to B, E, or C body backing plates brakes adn drums. Note this option widens the track by 1/2 on each side of that matters to you.