To cut cowl holes.
1. mount engine
2. tape pieces of printer paper to fuselage to extend over engine
3. cut paper to where needed for engine, exaust, needle valve ect...
4. remove engine (leave paper in place)
5. install cowl and mark where to cut using the paper cutouts as a guide.(paper should slide over outside of cowl, ie.. slide cowl under paper.)
6. remove cowl, make cuts, imstall engine, install cowl and make trim adjustments as needed.