So after sanding and doing a little trimming to get the fronts of the cowls lined up it is time to put the top cowl on and trim length. So I followed the plan's suggestions of drawing a line 2 inches back from the front. But I put a line of tap there. Recall my fuselage is painted and so tape worked better.
I made some 1/4 inch spacers to put between the cowl and prop backplate. They might have been more like 3/16. By the time I finished the cowl fitting this space shrunk to 1/8. I hope that is enough.
I did a bunch of reading about high low I should make the front of the cowl to account for engine sag and decided on none. The engine has been on, fully bolted for awhile now. And if the engine sags I can easily put a couple washers in the engine mount bottom bolts later to raise it back up.