Its a long process:
- mount engine.
- make a cardboard / paper template, STRAIGHT off of the fuselage, of where the head is, carb is, exhaust, thrust washer is <-thats important to get so you have enough clearance for your spinner.
- make sure you mark where you started all the measurements from on the plane and cardboard / paper.
- remove engine.
- mount cowl a little behind where the thrust washer would be located.
- using the marks you made on the template and fuselage, mark the cowl.
- remove cowl.
- using a small drill bit, drill into center of !QUOT!engine head area.!QUOT!
- don't cut to you lines yet, mount engine and test fit, trim as needed.
- a dremel works the best to open and clean the hole.
- just take your time and it will come out good.
good luck
Ron