With the propeller shaft hole cut out of the upper and lower cowling, I made my first test fit. With both cowling pieces in place, I traced the aft line of the cowl to the forward top skin and forward fuselage side skins to see how much excess cowling material there was in the back. This also seemed like a good time to finally trim the excess material from my forward fuselage side skins.
For each side, I marked a line from the front edge of the forward top skin parallel with the firewall rivet line to the bottom of the side skin. Then using my trusty Olfa knife and a straight edge, I scored the side skin about 20 times as was able to snap the excess skin free with a couple of bends. After some filing and sanding, I had two trimmed side skins ready for fitting the cowling.
When I had the cowling in position, I found the cooling hole flanges interfered with the baffles forcing the top cowling to press against the back of the propeller spinner mount. After estimating about 3/8" overlap between the baffles and top cowling, I removed the cowls and trimmed the top cowling cooling hole flanges with a dremel. After reinstallation, I found I had improved the spacing with my trim estimate, but I still had another 1/8" or so to fit it properly. I'll get after that next time.
Right fuselage side skin trimmed. Left side (background) still requires trimming. Removed 3 to 8".
The flanges on the inside of the cooling holes interfere with the baffles requiring trimming.
After initial trimming: Upper cowl still sticks out ~1/8" beyond lower cowl.