After additional research, I'm informed that the AC compressor on this 67 C Code car must have been replaced at least once, since the one installed on the car now has a York flange-style fitting configuration on the cylinder head, as opposed to the correct Rotolock fittings that were original equipment. (Or maybe only the head and valves were swapped at some point). Anyway, I'm leaning toward a new York Rotolock compressor instead of trying to rebuild the compressor currently on the car.