converting smallbolt to large bolt

You're going to need more than drums.

A body SBP drums were 10x1.75", and there isn't a big bolt pattern drum for that size. Large bolt pattern axles also use a different offset, so they won't even work with 10x1.75" brakes.

If you're buying axles, your best bet is to find a set of 10x2.5" rear brakes. You'll need everything from axle housing out- backing plates and all.

Easy enough parts to find, Ma Mopar ran 10x2.5" brakes all the way up to the 90's. They're in wrecking yards everywhere.

If you're not the wrecking yard type, shoot me a PM. I've got a couple sets of 10x2.5" brakes laying around I can part with for cheap.