"HELP" Power brakes very touchy

i'll roll some dice and say that it's probably the master. i'm guessing you bought one of those "universal" ones they sell that's based on the corvette master and the bias is all wrong.

or as mentioned up thread you may have a drum/drum master
No, it looks the same as the original and bolted in without any modification. Here is the link.
1963-1974 Dodge / Plymouth Mopar A, B and Chrysler E Body Brake Boost