Disc Brake cross-over?

most rwd spindles will bolt onto other rwd cars (A,B,E,F,M,and J bodys) however drum brake A bodys do use a different upper ball joint so you would nead A body disk brake uppers. some bigger B bodys in the late 70s (Magnum cordoba ect) had larger rotors, but still used the same spindle and caliper .they had a spacer to move the caliper bracket out an extra inch or so. there were 2 basic styles of caliper, one used pins to hold everything together, the other (more comin) design was the caliper sliding back and forth on the bracket. I do believe there were different sizes of pistons, and also some ceramic and some metallic pistons depending on the application.
obviously this is a brief explanation of front brake interchangability tell us what your wanting to do and hopefully we can help