If the perches line up, its an A-body rear end unless the perches were moved. Same with the SBP axles. They only came on A-bodies.
Here's the bad news. If you're going to use the SBP axles, you MUST find backing plates that are for SBP drums. Nothing else will fit. BBP drums have a different offset on the backing plate, and can't be used with SBP axles. So even if you find a set of 10" backing plates, you have to be sure they're for SBP drums. That also severely limits your ability to find rear drums, as I believe there's only one or two places left that sell SBP drums.
I don't know about the SBP 7.25" backing plate, but I know that the BBP 7.25" backing plates are the same as for a BBP 8 3/4, you just have to drill out the 5th hole. The other 4 bolts line up. But that may be different on the SBP 7.25", because they don't actually swap parts with a BBP 7.25".
