The pump driveshaft goes in from the BOTTOM!! Stick it up through the hole (distributor) and then put the pump on. Once the driveshaft is in, and before you button everything up, get the priming tool and put it down in the hole and spin it by HAND to see if there is a slight drag. That should tell you if everything is cool.
I did this once in my car. The oil pump let go at 6 grand at the big end of the drag strip! It twisted the driveshaft so bad that it looked like a drillbit when it came out! It was very hard to do with the engine in the car. A couple of years later I rebuilt the motor and have had the motor out a couple of times. I know it sounds backwards, but it takes less time to pull the motor, change the pump, and put it back in. It took me a weekend to change the pump in the pan and it only takes me about 2 hours to pull the motor and 3 or so to put it back in.
Oh yeah, thanks MOBIL 1! After the pump went, the car still ran and made good oil pressure for 2 more years. When I rebuilt the motor, the bearings were like brand new!