I have a set from a 70--but are you talking about the grease seal piece or the backing plate itself. When I took the 70's apart there was a small metal piece that seems to be meant to catch any grease that gets past the seal. That part disformed because the bolts spun on and disformed it, but it definitely is a separate piece from the backing plate for a '70. If you need the backing plates that the shoes are attached to, I have those...
Sounds like you had the same problem I did with the bolts spinning and messing the piece up. I guess I'll have to cut the bolts somehow to get it off I just decided after posting this that I'm going to do a disc conversion; I didn't realize it was so cheap. I appreciate the offer though.