Dean, I don't have this plane so this is general knowledge. If I was doing it, I would tack the mount(with thin CA) to the center of the FW over the center of the hole. Then test fit the engine and/or cowl to see what kind of fit you have. This should be the right place and you can drill. If not, you can adjust it from there. I would also fuel proof the FW first. This way the this CA can't penetrate to deeply. You can also this CA your engine to the mount while doing all of this..

David