What brakes to fit 15" cop wheels

I have a HDK front k member I will be installing and need to think about what brakes to run up front. I want to keep my 15" cop wheels, and will be using the stock disc brakes on the explorer 8.8 rear. So does anyone know what is the maximum disc size I can run with the mustang II front spindles and still clear the calipers on the steel wheels?

Also, what are my choices for replacing the HUGE power brake booster setup on the 74 dart, it takes up quite a bit of space that would be helpfull in my motor swap. I want to keep power brakes though