Trimming the cowling top half was actually interesting and fun.
First, I temporarily mounted the prop spinner back plate and prop spacer to the flywheel to give me a reference for mounting the front edge of the cowling. I used a sheet of 1/4" oak veneer from the Home Depot Aviation Supply Company to provide an accurate 1/4" space between the spinner plate and cowling.
Secondly, I marked about a dozen reference marks on the fuse skin exactly 2 inches back from the firewall flange forward edge. These helped me find the firewall forward edge underneath the cowling back edge when it was laid in place, giving me an accurate line reference for back-edge trimming.
I then used 3 pieces of 3"x1"x0.042" sheet aluminum to make temporary shelves I cleco'd to the firewall flange. These hold up the cowling's back end once I had trimmed the edges.
With the forward spacing good, I then used 0.063"x 3/4" angle to make a small shelf on the oak veneer to hold the cowling front end at the right height. This is where I ensured the prop spinner sat slightly high, which will allow for gradual engine droop over time.
