The drive shaft/gear is probably not seated all the way. The flat "blade" at the bottom of the gear/shaft has to fit into the slot in the shaft at the top of the oil pump. Have an assistant put a wrench or socket on the front pulley to turn the motor while you put pressure down on the gear--you may have to "rock" the motor from the front pulley (or tranny in gear--pushing the car back and forth). If you want the distributor to sit in it's original position you must set the motor to TDC firing stroke for cylinder #4 and refer to photos in the repair manuals as to the angle of the distributor drive gear slot relative to the block. Then take the gear/shaft and hold them near the block so you can see the direction of the bottom blade. Now take a long screwdriver and insert it into the oil pump drive and turn the pump slot to the approximate right position. Remember that as you insert the gear and shaft into the motor you have to compensate for the amount it will rotate as it engages the gear on the cam. -- Dave