mjd3, As far as trimming be careful with the knife, if you come across a soft spot, it is real easy to slice off more than you want. If you use a dremel, use a sanding drum and take your time. To locate the holes, mount the engine and tape some card stock to the plane and lay it over the needle valve or glow plug and make a mark on the paper for what you want to cut out. Then leaving the paper in place, remove the engine, mount the cowl and mark the cowl with the marks from the paper and cut.