Drum to disk brake conversion
I did this change last year to my GT/CS. I had bought a totally rusted out GT/CS to use as a "parts" car, and took the disk brakes off of it and put it on my "driver" GT/CS. The only problem was that this is twice the work! (You have to disasemble / reassemble both the parts car and driver car). If I had not found the parts car, I would have used a kit from Stainless Steel Brakes or Master Power Brakes, or some other vendor to take advantage of newer technology.
If you are building an MCA councourse vehicle, then you will need to find original Ford parts from a donor car or Mustang vendor or e-bay.
I live where it rains quite often (Hawaii), and everthing I've ever seen about drum vs. disc brakes said that discs are better in the rain.
Just my $.02
Harry Z.