Turn the engine to TDC and check that both rockers on the front cylinder have slop in them. If it's the ones on the rear cylinder that do, turn the crank one full revolution back to TDC. The drive gear should look like the bottom right photo here:

http://www.1800philes.com/docs/files/?chapter_id=17&file_id=707

If it does not, pull up the gear so you can turn it, and start it back in so the slot is almost perpendicular to the block and offset towards the rear. It will not drop all the way back in because the oil pump no longer lines up.

Turn the engine while applying light finger pressure downwards on the gear, and it will eventually drop all the way. Turn until you have TDC with lash in both front rockers again, and check the orientation again. It will either be right, or one tooth off.

Repeat if necessary.