So I just stole some great brake info from here
Master Cylinders FAQ
here are some highlights
Do disc brakes require more pressure than drum brakes?
Yes.
Can I run disc brakes with a manual brake master?
Yes. The bore size of the master can not be larger than 1" and your leverage at the pedal has to be greater than power brakes.
If I add disc brakes will I need a proportioning valve?
Yes. The addition of a proportioning valve is a must. Without it your braking system will not operate properly.
How does a disc brake master differ from a drum brake master?
A drum brake master will differ from a disc brake master in two ways. The amount of fluid that a drum brake master has to move is less than disc brake. Drum brake masters have 10 lb residual valves at the outlet to keep a residual pressure on the drums. If you use a drum brake master for disc brakes you would move an insufficient volume of fluid and the disc brakes would drag because of the residual valves.
Can I use my manual master on a booster?
Yes.
Why is one fluid chamber larger than the other in a disc/drum master?
As disc brake pads wear the caliper pistons will move outward. The fluid level in the master will drop more rapidly than the drum portion so you need more reserve.