the drive gear goes through a bushing in the block, then indexes in the oil pump drive[ 5/16" hex at the end of the shaft]. observe how the drive gear is in relationship to the cam gear to get an idea how far the two gears mesh with each other. then, as has been stated, use a very large flat tip screw driver to "unwind" the distributor drive shaft from the cam. position the drive gear as you want, then screw it back into the cam gear with the slot pointing as you need it to index your distributor for the amount of adjustment needed. not as difficult as it seems. just make sure the gears are meshed properly, insuring the hex at the oil pump drive is properly in position. if the distributor does not seat on the block, you know the drive gear is not engaging the oil pump properly. just may need a little fiddling, but the only way you can mess something up is by forcing things together. hth.