1965 Valiant low brake pressure

OK, lets start with the basics just to make sure we dont chase something simple for days. Are you sure it is a drum/drum MC and not a disc/drum? ( no, I dont doubt your intelligence but i do doubt the intelligence of autozone employees). did you bench bleed the MC before you hooked it to the rest of the system? did you start bleeding from the farthest wheel from the MC? are the bleeder screws all in all the way? (not just tight, one might have gotten stuck part way allowing air in)

and did you wait for all the little air bubbles to stop coming up from the MC?