My 8 3/4 is out of what?

I need to order the complete brake assembly for my 8 3/4 but NAPA (and me) need to know what car they fit and Im not sure.
It has the SBP, I measured from axle flange to flange and its 56 3/4, I looked at measurements I got off of mymopar and they list a 56 7/16 flange to flange so Im pretty sure that is what I have. Mymopar list it as either a 69 c body or 70-74 e body. I do have the backing plates and a set of shoes that came with the 8 3/4. I can measure the shoe size if needed.
Any thoughts on what car this would have came from?