New 10 inch drums on a 8 1/4 rear end?

Lots of options out there, but you'll want a set of 10x2.5" drums for it. They don't have to be B body though, 10x2.5" rear brakes came on pretty much every mopar out there up until the 90's. I suggest looking for FMJ body stuff, you can find them on Diplomat's, New Yorker's, 5th Ave's etc up to like 1989. So they're pretty easy to source from the wrecking yard. Just remember to take 5/16" socket or wrench for the retaining pin in the 8 1/4 rears so you can drop the c-clips and pull the axles.

Shameless plug- I have couple of 10x2.5" brake set ups, they'll fit in a flat rate box. Pm me if you want a set, I'd be happy to let them go for cheap.