Brake booster - drum vs disk

[Vortech]

Ok, Planning on upgrading from single pot master cylinder to dual pot with booster. Question, I've found one at a local wreckers off of of 71 pick up, but has front disk brakes. Can I use this set up and just omit the proportioning valve in order to work on my 4 wheel drum set up?

[blown240]

Usually a disk/drum brake master has a large and small side to the reservoir, and a drum/drum has 2 sides that are the same size.

The booster is the same either way.

[luvbowties]

You can try that and if rears lock up too early, you can always plumb in a 'freestanding' prop. valve(approx. $50.00 at Jegs, Summit, and others) into the rear line to decrease its pressure to proper bias.
Sounds like the oem prop. valve is missing: if it's there, grab it for when you add disc brakes to your front. Those short, nicely bent, curled lines are just too difficult to duplicate.
Sam
BTW: Iirc, in 1971, front disc used same master as non-disc, like in 1970.

[Vortech]

so this set up has the prop valve, do I keep it?or omit it?

[60ShortStepGMC]

Omit the prop valve for drum/drum set up.

[Captainfab]

Why not just get the correct '67-'70 drum/drum master cylinder at your local auto parts store? You will need either a different booster or go with the '70 Buick Estate wagon master cylinder on the '71 booster.