Kurt,
you could certainly upgrade your single master to the dual master and keep drums. Some early 70's vehicles still ran that way. The dual MC gives you more security in case 1 brake line blows you dont lose both front or rear brakes. The prop valve is adjustable to adjust front to rear braking.
A front disc/ rear drum set up also requires residual pressure valves (RPV) also.. discs require only 2 PSI while Drums require 10 PSI.
Since you are separating front and rear brake lines, plus adding RPVs you will be running some new lines. Not a bad idea.
I actually purchased my non power MC from Old Dog Street Rods in STL. They had a bracket which bolted to my frame under the cab. I found later it is a Corvette MC and primary/secondary wells are reversed. Not sure why this is a good thing, but works well with Old Blue.
yet one more source for disc brakes is Speedway motors. Their catalog has diagrams which help explain the brake line RPVs and prop valves.
I am running 15 inch Ralley wheels and have good clearance.
