The
oil pump drive shaft must be rotated about 20 degrees, or if you have the distributor in and it is properly lined up (except for the last few degrees) but not fully seated; you can press downward on the distributor body and either have an assistant tap the starter switch or use a remote starter button. The engine will begin to turn over an pull the ditributor body instantly down to fully seat it in the block. An alternative to both of the above is to use a 2nd distributor with the gear removed or a shaft from a donor distributor and insert it into the block and rotate the
oil drive shaft a few degrees at a time, while repeatedly trial fitting the distributor. Be carefull when removing the distributor each time and be sure the shaft is not pulled out of the
oil pump (youl'll hear the dredded "Clunk"). A combination of shaking/rotating the rotor while slowly removing the distributor will avoid this. With a little practice this becomes pretty easy as long as you realize what as to be acomplished for things to line up.
A word of caution:
If you accidently pull the shaft out of the pump, it is somewhat difficult to get back into the pump without pulling the pan and spoils what would normally be a simple job.