I agree with Chris that (1) You've got stuck adjusters. I had one recently that I was able to un-stick by taking the drum off, spraying liquid wrench on the threads of the adjuster, then working it with vice grips on the adjuster; (2) Replace or rebuild is even better; (3) disks are great in that (a) you don't have to deal with adjusting and (b) if you break a rear axle it won't walk out on you.
BTW, disk calipers can stick too. BTDT. Disks can fade with heat, BTDT also. And drums can be quickly dried by riding on them lightly just after your water crossing, works fine unless there's a huge hill climb on the other side of the creek. IMHO the biggest downside to disks is initial cost, they're a major chunk of change!
Matt, I did not mention in my article that some cruiser drum setups have one bleeder per wheel, yet still have two cyliders. Both cylinders are bled from a single bleeder port. My 71 has a port on each cylinder, but my 78 FJ45 has only one, even though it has two cylinders per wheel. I can't remember which setup my 76 has, it's been a while. I do know my 76 has two cylinders per wheel though. You can see the photos on my resto pages. The single cylinder per wheel setup was not introduced until 1980 when the parking brake was moved to the rear wheels with the introduction of the split case.
In any case, it sounds like your biggest issue is a leaky booster. To give you a frame of reference, I drove mine with a leaky booster for a year or two before I burned up my valve, so it's not an instant death thing. I was still able to drive home on 5 cylinders, but the little pieces of valve sound like hell rattling around in the combustion chamber! It cleaned up the carbon really well though :-/