Another idea is what my dad did to his 70 back when it was nearly new. He got a 5 lug hub and had the 4 lug drum redrilled to fit. That way the car retained the smaller drum and backing plate. Not sure of the specifics as to how he did it nut it sounds pretty straight forth. The car was that way for 20 years.
I was thinking of getting it re drilled but I didn't know of a place that would do that. Do you think that Duralast would do it?