SBP to Big Bolt Conversion

I'm assuming you already have discs, but they're the early Kelsey/Hayes with the small bolt pattern? If they are working well and you're satisfied with them, and are only looking to get the big bolt pattern, consider keeping them and just replacing the rotors with early Mustang (yeah, I know) K/H rotors that have the 4.5 bolt pattern. There's a different inner bearing and seal to use if memory serves me, but a quick search should turn up the info you need. Much cheaper and easier than swapping over the whole system.