brake shoe source

Look on your original shoes for the FMSI number. Usually stamped on the steel somewhere.

Sometimes the parts suppliers substitute alternate frames/backing plates that aren't really right. Sometimes they will work, sometimes they won't. Sometimes, if they are for a later setup and the backing plate hadn't changed, you "just" need to switch to the later hardware.

Off the top of my head '69 and up 10x1.75" rear shoes are FMS 331 and the wider 10" shoes from a few years later are 333. But don't rely on my memory.

Worst case is hunt on-line for the right FMS number or get yours relined by a place like Rochester Brake & Clutch or Porterfield. A bonus is they can arc them to your drums.