1964 dart brake problems..

Power or manual brakes? Assuming the brake system is the original single pot master cylinder and it’s still drums on all 4 corners. When you bled the back brakes what was the fluid flow while bleeding? Less on right rear than drivers? It could be the port on distribution block off master cylinder, or splitting block on rear has junk in one or other restricting fluid flow. Could very well be the wheel cylinder is the issue. But the cylinders have to have good fluid volume to operate any restrictions will impact them. Another issue could be the shoes are not adjusted tight enough to push fluid every where in the system. Did you bench bleed the master cylinder before installing? Just some thoughts off top of my head where I’d look, fishing for information.