Can't Stop 71 440 Demon

Working on a 71 Dodge Demon 440 4spd.
It has 4 piston calipers which are not rebuildable. I have been looking high and low and every parts supplier states that these are no longer available or that they can get one side but can't get the other.

My question is has anyone switched from 4 piston power brakes to single or dual and what is involved?

Sucks that car is finally running but I can't drive it cause it wont stop.