Help with brakes.

Yeah, just about any old M/C can be made to work.
To test the booster, you sorta gotta have a hard pedal to start with.
To get a hard pedal with drum brakes is easy but takes time. You HAVE to start with a bench-bled M/C. Without residual valves this sometimes takes a trick. The fluid likes to return to the reservoirs just as fast as it goes out, so you sometimes end up frustrated with fluid just shuttling back and forth. To prevent this, you gotta pinch the lines before allowing the M/C pistons to return to their parked position which is when the additional fluid gets sucked into the power chambers thru the compensating ports.
Furthermore, there is a chamber between the front and rear sections of the M/C that has to be filled up during the bench-bleeding procedure.
Furthermore, the frontmost reservoir has to be plumbed to the rear brakes.
Furthermore, the front and the rear brakes have to be isolated from eachother. Well they don't for functionality, but that defeats the purpose of having a dual-brake system.

The best way IMO to isolate where the problem is, is to do one of the following;
1) adjust the **** out of the brake-shoe adjusters so the shoes cannot budge, or
2) remove the drums and all the hardware and C-clamp the metal plugs into the wheel cylinders so that they cannot budge.
All the fluid in the system is theoretically thus locked from moving. If the air is out, the pedal will do one of three things;
1) be hard as a rock; this is what you want
2) be spongy; this indicates trapped air somewhere
3) be soft and sinking to the floor, this indicates fluid transfer within the M/C and is bad. You may be able to take the M/C apart and discover why this is happening and even to fix it, on account of those things are pretty simple devices.

The booster will throw a bit of a monkey wrench into the mix, as the Push-rod coming out of it has to be adjusted within a very narrow range.
If it is too short it will not stroke the Piston assembly inside the M/C far enough, and you end up with insufficient fluid travel out of the pressure chambers to affect proper braking; the pedal will reach the floor first.
If the P-rod is too long three things can happen;
1) the C-port will not be opened at the pedal return and eventually your pedal will go lower and lower to the floor
2) the braking will begin too early with respect to where your pedal is and boost will be rather abrupt. This will take time to get used to and different drivers will hate it.
3) if it is much too long, you can break the control valve in the booster, and then you lose modulation. Instead, the booster will full boost with the slightest pedal motion away from being parked.

Somewhere in your system should be a light switch to turn on your brake warning lite on the dash. This thing is operated by a fluid differential between the front and rear systems, to tell you if one end or the other has failed. This device has fluid from both reservoirs dead-headed at either end of it. During the bleeding procedure it is possible to push the valve inside the device from one end to the other. This shuts off the one side so you don't pump brake fluid all over the street after one end fails, and makes sure the other end still functions. And it turns on your dash lite by grounding the circuit. This same lite is used to indicate that the Park/Emergency Brake is on. So if your lite is on, you better know why that is so. Now the point is this, if someone failed to install this device, you need to get one. Or if somebody has removed the valve inside of it, you need to install a different one. Or if yours is stuck at one end and you cannot turn the lite off, you need to fix that.
Now, by this time it should be clear to you that the front and the rear systems are supposed to be independent from eachother, and the only possible connections between them are at the Safety-switch and in the guts of the M/C.
As for the front brake system, they are split usually at the drivers side front frame rail, but both front W/Cs are connected to the same rearmost reservoir. So if one side fails, you will lose Both front brakes.
This makes your description of bubbles at both the front and the rear bleeders on the ONE SIDE ONLY, a real puzzle. My guess is that somebody cross-connected the two systems, and that your car may now have the left side operating off one reservoir and the right off the other; this is bad, so
check it out. But it's just a guess. It could just as easily be, just not fully bled, or,
When you lift off the brake pedal during the bleeding procedure; it is possible that the fluid returns to the M/C faster than your brake return spring return the shoes. When this happens, the M/C may gulp air at the threads of the bleeders. To prevent that I remove the bleeders, clean the threads, and the bleed hole, then anti-seize the threads. Then during the bleeding;
I connect a small clear flexible plastic line between the just-barely cracked bleeder and a small reservoir and elevate the reservoir as high as I can, to a max of say 12 to 15 inches. Now I can see if the fluid is just shuttling in time with the pedal, or if there is in fact air coming out, AND I know it ain't coming from the backside of the sealed-by-anti-seize bleeder.
I find the residual valves handy to slow the return of the fluid.
After the beast is all bled, and the shoes have been properly adjusted, then the brake return springs will control the fluid return. I wouldn't waste time and money installing residuals if yours are not there, AND your W/Cs are not original-type.