I would recommend at least changing the master cylinder. The reason is that the original equipment only has one line coming out of it. There is no fail-safe. The new ones have two lines - one for the front brakes and one for the rear. That way if something goes wrong with, say, your rear brakes, at least you would still have front brakes - for a time - until the fluid all was pumped out. At least you could get stopped safely.
You didn't say what you are doing with the front brakes/suspension. Will it stay stock? If so, then I don't know about putting disks in back with drums up front. I have never heard of that before, and probably with a reason.
Good luck!
Craig
