Brad, Your bolt down M/C is for drum brakes only.
With Disk brakes on the front, you have to go with a disk brake master cylinder. For my Cuda, I just went to AutoZone and got a lifetime warranty one for a 72 Cuda. Everything around then was available without power assist. You might try one from a 73 Dodge Dart, non-power, disc brake. Try Oreilly's, Advance Auto, Rock Auto, etc. Mine was less that $20 when I got it.