I have all four drums on my '74. Everything cept lines and shoes is brand spankin new other than booster (which is still fine). Whenever I go through some deep water, my brakes pretty much quit working and feel like manual brakes for a very long time. (Takes 1 day 1 night of sitting to fully dry them,) or less when driving a lot. This has caused me to have some very close calls, especially last weekend when we had a tornado and and inch of rain in half an hour, I drove through some 3 foot deep water and then almost had a few wrecks cause I couldn't stop.
One other brake problem, whenever I have to slam on the brakes, (not necessarily that hard) the rear brakes instantly lock up, causeing me to skid pretty bad, also causing a few close calls. When the roads are wet its hard to stop quickly at all without locking up the back. Something that might be related-the first brake to dry is always the rear left, I can tell cause right after I go through deep water and have to brake firmly, I always swing to the right. Any help is greatly appreciated, this is starting to get dangerous
sometimes. 
One other brake problem, whenever I have to slam on the brakes, (not necessarily that hard) the rear brakes instantly lock up, causeing me to skid pretty bad, also causing a few close calls. When the roads are wet its hard to stop quickly at all without locking up the back. Something that might be related-the first brake to dry is always the rear left, I can tell cause right after I go through deep water and have to brake firmly, I always swing to the right. Any help is greatly appreciated, this is starting to get dangerous