I was doing a lot of disc brake conversions on the 57-61s years ago. 70s A Body spindles, rotors and calipers can be made to work fairly easily but require modifying the tie rod and tie rod sleeve and steering stops. 77-78 C Body spindles, rotors, and calipers will also work but in addition to the tie rod/steering stop modifications also require a modification to the spindle and selecting the correct ball joints. The geometry of the A and C body spindles is not an exact match to the original spindles which will require an alignment afterword and you end up with a little bit quicker steering.
I think AAJ was about the first outfit to offer a conversion using the stock spindles. I have that conversion on my 57 Plymouth and would use it again if I were building another car of this era. As I recall they use A Body rotors and I believe GM Calipers.
http://www.aajbrakes.com/rproductinfo.htmlI haven't used the Scarebird stuff, but have heard good things about them and you do end up with bigger rotors. With AAJ or Scarebird you end up with a lot less work (and if you car is correctly aligned save a trip to the alignment shop).
