small block oil priming question

only vac advance changes rotor phasing. If you drill a 1/2" hole in the top flat of the dist cap 2/3 of the way from the center tower to the #1 tower. pull/plug the vac adv hose & look down at the rotor with your timing light & gun it & the rotor does not move. plug the can back in & repeat & the rotor does move.