Master Cylinder Change?

If you get an older MC, insure it doesn't have "residual valves" in the outlets. I understand most are removable (haven't seen). That is the problem with "locking up pressure" you read about if using disk brakes. Indeed, they aren't even needed for drum brakes since they changed to the "spring w/ caps" design.

I suggest a modern aluminum MC to save weight. I put one on my Dart and Valiant. Cloud car MC's (Breeze, Stratus) until ~1999 have standard 1/16" double flare outlets on driver's side, which is best (bubble flares are trickier). I used an MC/booster on my Dart w/ 73 standoff brackets and a manual MC on my Valiant (not installed). The later usually means a 4-2 hole adapter ($45), but I just drilled 2 holes thru the firewall/brake bracket w/ a big washer covering the gap. With disk in the rear, you don't need much reduction in pressure (if any), so don't use a fixed factory valve but rather an adjustable one, and adjust it by locking up the brakes on a wet parking lot (fronts should skid first).