I replaced both rear rotors and the left rear calipher on my '71.
The new left rotor went on snugly with little effort; I did not have to loosen the parking brake shoes. The new calipher is a stainless sleeved one from Muskegon Brakes. I reused the old pads.
After test drive (about 30 miles of highway and stop and go), I could feel radiated heat 5-6 inches from the left rear wheel rim. The new calipher was very hot to the touch. The rotor was also hot to touch. The right side was cool.
Is this common until the calipher, pads and rotor "break in" over a number of miles? If not, is there a fix?

your caliper is not releasing,when you bled the brakes did you notice that rear caliper not getting much brake fluid? youve probably got a plugged brake line,it let the fluid into the caliper but wont let it back out.those rubber lines will plug up solid when they get old,they might look good from the outside,but they turn into jelly inside,then plug up and wont pass fluid,the same thing happened to my 78 last fall,on my last short trip downtown b-4 I put my car in the garage for the winter.

Thanks Ron 78 for the reply.

To close the loop on this thread: Replaced the rubber hose just as Ron78 suggested. The hot brake is no longer hot. I'm up and running.