Master cylinder

[CURSED GEARS]

Greetings gang.

First off, let me say I have a 70 Chevy long bed truck. I tell you this so you dont think I'm just here fishing for advise on a non related project. Now for the problem.
I've pretty much just finished a 7 year project on a 39 Chevy truck. Its a hot rod, and has several parts from different manufactures, (chevy Ford, Dodge) Anyway, during brake design, another site I'm a member of reccomended the 67-72 Chevy master cylinder for my project. I guess the bore size is correct for the wheel cylinders I've used. Anyway, I can't seem to get any real pressures to the wheels. The pedals not hard. I push the brake pedal down and dont really get brake until near the end of the pedal.
The master cylinder was bled, and the rest of the system was bled several times. The shoes have been adjusted until they drag on the drums. I have drums front and back, and the master cylinder is drum/drum.
My question to you guys is, for you guys who are running drum/drum brakes, do you run a residual valve? I've cracked open my rear bleeder screw, and nothing leaks out. There is no pressure on it at rest. I'm wondering if a residual valve would help.
Second question is, Are the chambers on the master cylinder specific? That is to say, is the front chamber for the front, and the back chamber for the rear? Does it make a difference?
I know theres a lot of sharp guys on here, I've been on this site for years, and I would appriciate any advice you might have to give.

Thanks,
Cursed Gears.