Ok, here is the update. Do not ever put your hands into an APC prop on a Saito 180, it will remove your fingers. I now have a new nickname "chopper". Ok now to the situation at hand.

I have just hung the DA 50 on the front of my Edge 540, as illustrated by the pictures below. I got my stand off from TBM and they worked perfectly. Now I come to the part where I have to cut the cowl to fit the motor, and this is where I become fearful of my building skills. the back plate of the spinner is 11 1/4 inches from the filrewall, and the center of the muffler canister is 5 1/2 inches from the firewall. How would be the best way to guage the exact place to cut the cowl?