Master Cylinder for Manual front disc, rear drum set-up?

You should not use a drum/drum master with front discs. The Raybestos is a good one for the application. Mopar used a 1-1/16" bore for manual discs in A-bodies, but that makes for a much stiffer pedal than most people are comfortable with. 15/16 bore reduces the pedal effort to a more reasonable level.