First time having manual brakes, are mine bad?

The reservoir has nothing at ALL to do with the immediate function of the brakes, how well they stop, the pressure generated, put that any way you want

My car is still "apart" but when it was running I had 73/4 Duster/ demon disk up front, and a Linc Versailles disk brake For 9" out back. "Just for to try it" I left the bone stock DRUM '67 master on the car. They have residual valves which I COULD HAVE left alone for a test, but I punctured them with a nail and ran it. Worked GREAT

THE ONLY CAVEAT with "equal" halves of the reservoirs is that A: It usually means a drum master and that you have residual valves in both outlets and B: that as the pads wear you must be a "little" more diligent about monitoring fluid level because there is less of it to take up for pad wear

Other than that THEY WILL WORK FINE if the BORE is within reason

Things I would keep in mind:

1...I have no idea if 15/16 is what you want for bore, do some research
2...REthink your pad/ shoe material Maybe the shoes / pads are glazed or poor material.
3...REcheck if the rear drums have been turned oversize HAVE THEM MIKED if you can find someone who knows how and has a drum mike

If none of the above pans out, it is time to buy some fittings and a pressure gauge and see if you actually have decent pressure at both ends. "I suppose" it is possible that such hardware as the warning switch, prop valve, etc has a problem, I would think this is rare

There "are guys" who claim that hoses can swell and plug when old, but I have never seen this happen.

Is it possible that you have calipers that are all rusted up? Can you move the pistons, or have you tried? Remove calipers, use a big "C" clamp and gingerly clamp into the middle of the piston around the back of the caliper. If you don't get the thing off center and wedged, it should move fairly easily