just 'tap' the key "on".
Use the engine/battery to do ur wrk.
Do not start the vehicle, just 'click', tap, jog the motor - quick on/off.
Do it several times till the gears in there line up w/the centric on the pump's arm.
I'd put a gasket on the pump w/a lill 'snot', 'glue', whatever's an appropriately designed
adherent.
We assume U R using a mechanical pump & placing it on the motor.
(B nice to have a buddy or wife do this while U struggle under the hood).
B careful of any rotating assembly catching clothing or skin & causing damage
8^0
"...don't remember exactly why..."
increase life of oil pump cam/cenrtic on pump?