Hy 48bomb, you could use a master cylinder intended for either full disc or disc/drum and install resisdual pressure valves in the lines/ports that were intended to feed disc brake calipers. I did find a 1 1/4' bore master with the same porting as the one you have currently, Raybestos p/n MC36359, currently available at RockAuto. I have no idea of the original application, so you would have to find that out and plan on the resisdual pressure valves if it is a disc or disc/drum original application, hope that helps.
