I'm afraid the oil pump driveshaaft was supposed to be installed when the engine was "upside down" on the stand. Not all is "lost", though. This happens occasionally.
Grind the two little "titties" off the shaft. Get a "screw starter" that's large enough to hold the shaft tightly in the slot where the distributor shaft goes. Lower the shaft carefully into the hole, and rotate it slowly until the "lugs" line up and you FEEL the pump turn when you turn the driver. Release it. Anoither tool that works is a fairly powerful magnet with a "flat" surface. You can hold the shaft that way, too. Once it's engaged with the pump, slide the magnet to the side until it releases.
If the "dots" on the cam and crank gears are at 6 and 12 (o'clock) respectively, you are "up" on #6 "compression". That won't "cut it" when installing the distributor. The gears should have both dots at 12. THAT is "up" on #1. If the timing cover is already installed, remove the plug from #1. Put your finger in the hole. Rotate the crank until you feel compression escaping. This is called "blowing number 1". Continue to rotate until the timing mark is pointing at "0". You are now "up" on #1.
When actually installing the distributor, the oil pump drive can sometimes be an adventure to "engage". The easiest way is to have some light pressure on the distributor "down", and "bump" the starter until it drops all the way in. This takes two people... If the flange on the bottom is not flush with the block, it's NOT all the way down. Another way to "line up" the shaft is to turn it slightly with a large screwdriver and retry until it "goes". All the while, make sure when the rotation of the shaft stops, the rotor is pointing "at #1" on the cap.
Good luck and let us know how it comes out.