Hints
Gary,
Following Dan's lead, I used my spinner to cut out a 13 inch circle complete with vertical and horizontal perpendicular lines. I used it to measure the initial amount I would need to cut from the upper and lower cowls to begin mating them. Keep everything as square as possible. You'll see how far you need to cut from front to rear just to get the top/bottom halves to overlap on the sides.
In hindsight, if I had used a laser level in vertical line mode it would have helped square everything up.
I noted that the cooling air inlets were not perfectly symmetrical, so watch that. Fit it together as best you can with the sides overlapping. This will get you started. I left mine a little long (every so slightly elliptical) so I could trim it to fit incrementally once it was hung.
Another tip using the laser level: Level the airplane fore/aft and side to side. Mount the top or bottom cowl as best you can (overlap in the rear is okay as long as it is close. Set up the laser level with the beam directly across the tip of the spinner. That defines your center line and helps position the cowl level from side to side.
I was lucky as I borrowed a laser level and found it very useful for fitting the cowling, even marking the sides, so the laser line bisects the spinner tip all the way back to the firewall.
Don