Maybe I'm missing something here. Why do the brakes have anything to do with a k member swap? He's got the 73 up suspension already. Switching to the '71 k frame doesn't change the brakes he can use.
Kid has another thread going about buying calipers, and from what I gathered it was kinda expensive.
IMO he would be money and time ahead to just do the Schumacher upgrade and run with it. The set up he has now is drivable. Pull the engine, upgrade the mounts and drop the 360 in.