the issue with the later calipers is the way the hoses mount. On some cars, there is a banjo mount (like the 73+ slider calipers), and others use a NPT fitting. Sometimes that can cause the hose to bind. I have stock 71 calipers and hoses on my car, I used the 76 - mid 78 pin type adapters, and I'm using the 71 spindles with the Dr. Diff bearing spacers, and generic Advance Auto Parts rotors.
I've done the swap from small disc to large disc twice now (79 diplomat, 71 challenger) and the braking is noticeable already. Can only imagine from a drum setup.