The way I've found to cut out "any" cowl is this....... What I do is to put masking tape on the side of the fuse just aft of whatever on the engine I want to have a cutout for. Then I use a ruler to draw a line over to the item that needs the cut out. I then measure back from the cut out item about 2,3, or 4" and make a mark on the masking tape. Then place the cowl on the fuse and place the ruler on the tape line and use your measurement that you made earlier to mark on the cowl where the cutout is going to be. I like to use a water soluable pens so I can clean the marks off later. This marking technique works great for stuff like the high and low speed needles, fuel dot's, exhaust, and the screws that hold the cowl on. For making a big hole for the engine cylinder I just approximate where and how much to cut out and take out a lot of the cowl material then try to fit it on and trim out more as needed. For the cutting I drill into the cowl with drill bits and then use a sanding disc on my Dremel. I also use a tapered reamer to make holes and enlarge holes to the exact size I want.