I know when I pulled my distributor and reinstalled it. I thought I had it set to number 1 on compression stroke, but it was slightly before and one tooth off., that one tooth syndrome strikes again.

While your timing it, pinch the vacuum line and see if it causes it to move off your mark. You will probably find the problem and kick yourself that you didn't find it sooner. It seems to happen here a lot. The distributor has a mark at the bottom of the unit. There is one on the distributor gear and it must line up with the one on the housing right near it. They are very tiny dot marks in the casting. Once you line these up, you have the job to insert the distributor without moving these two dots apart, otherwise you miss the drop. I would remove the cap and grab the dizzy top with the rotor and keep that rotor from trying to turn just before the dizzy makes it all the way in. It's kinda tricky and there is also a starting point for the dizzy that they placed on the head to line up with the mark on the distributor housing after it is installed. Mine kinda looks like it's one tooth after the number one electrode post on cap, but it's just the illusion. Felt pen the outer housing at number with a line helps to.