Rear disc brakes

Cool find. What is the diameter and thickness of the rotors? Are they solid or vented? Are the calipers single piston?

Not sure what master cylinder to use. But you should be able to use a disk/drum I would think. One thing to watch out for is that there is usually a residual pressure valve somewhere in the drum brake hydraulic system. Sometimes it's part of the wheel cylinders, but it can be built into the master or an add on check valve somewhere in the line. You will also probably need an adjustable proportioning valve to set the biasing properly.

Ohh, and what kind of parking brake setup did the donar car have? I'm pretty sure TxDOT requires a functioning parking brake for safety inspections.