manual front drum to KH disc swap

What you will usually end up with is a drum brake m/c (equal size resevoirs) with no residual valve in the rear outlet (feeds the front brakes). It will work fine, but itsbetter to get an m/c with the larger rear resevoir if you can find one. That way as the pads wear, there's always plenty of fluid. Also if you're road racing there's less chance of boiling. Minor issue otherwise.