I do not think there was a drum power brake set up. Not 100% sure on that. If you have disc up front and drum rear and say Power Disc on pedal you have PDB. The master cylinder is different on 72 & 73 for PDB being 15/16" dia. and drum is 1" 1971 all were 1". If switching to PDB the pedal is different and nobody had the original booster, Bendix. I build my own costs so much to sent to Oregon to get built. Usually not much wrong inside.
I should start rebuilding on east coast I have a fixture to take apart and assemble. I found all the parts after years of searching. I am out right now I just sent a member three sets over seas.
Lots to change going to PDB, spindles, hoses, hard lines, proportioning valve, pedal so know what you need before you start.