8 3/4 Disc brakes from Summit

I think the reason they stop at 1972 is because the 8 3/4 rear was replaced with the 8 1/4 rear the next year.
I bought the Summit brand, calipers are by SSB, but I don't have them installed yet, but I'll be working on it.

http://www.forabodiesonly.com/mopar/showthread.php?t=65875&highlight=summit+rear+disc

I have a 70 Duster. Hope this helps !