Removing distributor

Pending exactly how old and rusty it is, could very easily have rusted itself into the oil pump driveshaft. And the oil pump driveshaft could be trusted to the pump, the cam, etc.

Sounds like you are tearing it down to the block. Flip it upside down, pop pan off, take off oil pump, tap shaft our from the bottom. I'm obviously assuming you will be buying a new distributor, pump, and pump driveshaft.