I'm very close to firing up my Hemi.

Where does the vacuum advance and power brake go into the block? Behind the carb?

If they share the same plug on the rear of the intake, who sells it?

The vacume advance should be hooked to the right front vacume tube sticking out on the rear carb. on the passenger side front The power brake vacume hose will go to the bigger vacume fitting on the intake manifold in back of the rear carb. If that fitting has another small nipple sticking out of it that would, could be , the vacume source for the heater doors. I've never owned a stock 1971 non air conditioned Cuda so I'm not sure if the heater doors on them are vacume controlled or cable controlled IHTHs