Doesn't affect you since your car was 9" drums, but I found that ball joints varied between 10" drums and 73+ disk brakes. I bought the later ones since much cheaper, but found they have both a larger bolt hole and different spacing than the 10" drum ones on my 65 Dart. I sold them and got the correct ones ($60 ea Autozone, and later scored new Moog China ones for $13 ea).
It looks like you have a "combination valve", which has both a proportioning valve for the rears and an imbalance warning switch. You would have to install a dash light to use the switch, and need to center it correctly. I wouldn't bother since I bet most are frozen up anyway in most cars. The pedal went to the floor once in my 69 Dart and I never saw a warning light.