rear brake drums

That's because nobody has them. The small bolt pattern 10 x 1.75 rear drums are no longer being manufactured (at least by the normal brake vendors -- I don't know where those guys on eBay get them). So otherwise it's a matter of finding some from a guy that has done the LBP swap. Unfortunately, those guys tend to assume that brake drums are scrap iron and let them go to the recyclers instead of hoarding them as cash cows (as they should).

In the old days they used to reline drums -- maybe it's time to find a blacksmith who can do that. Seriously -- I'm in the same boat.

If you do find some with life left in them, do not ever use semimetallic shoes -- you don't want to wear them out. If you have to turn them, tell the machinist to do the lightest possible pass.