rear brakes get too hot

Since normally the front brakes do more work than the rears, the rears being hotter is a sign that they are doing too much, especially with the same sized drums front and rear.....is the the case for that car?

Not near any data for the wheel cylinders sizes; they would be in my old Chilton's book... that is 500 miles away. I assume the FSM would certainly have the sizes; is there one online for you? For the '67 with the stock system components, I would expect (just from general principles with the same F and R MC pistons) the front cylinders to be 1/16' to 1/8' larger than the rears.

I would not change the rear wheel cylinders unless they were the wrong size. The sizes are set to work with the car weights and MC piston diameters to set the basic F/R proportioning.

If you jack up the car and spin the wheels, are the rears dragging in any way? Also, any chance that this started occuring with the new MC? I am following up on RRR' thought about a residual valve; might be missing on the front and letting the front shoes back way off. But the pedal wold move more than normal if that was the case. Is the pedal action normal?