The best way to fit the cowl is to follow the plans. What the plans don't mention will become obvious as you start to fit the top cowling. The bottom goes fairly well.
With the top you will run into numerous interferences and issues mainly around the cowl inlets. Sometimes it is hard to figure out where the problem is, use a piece of paper and slide it around between the top and bottom to locate the tight spot. Trim slowly, it takes a long time to do an epoxy repair.
The cowl glass is actually fairly good, especially if you did a -6 cowl from the 80's. I essentially removed and rebuilt almost the entire inlet area of that one.
Rans S-20 Raven 796S flying since 2019 (slowly)
RV-6A 596S flying since '89 (Sold)
HP-18 5596S flying since '83
RV-10 996S flying since 2014, quick build wing and slow build fues., - dual Skyviews with complete system, two radio and not much else. Interior completely finished with Zolatone. CF plenum. 1624 lbs, FLYING after a 21.5 month build.