I haven't actually mounted my YS .91 yet (will do it today sometime) but it looked to me like you could mount the engine inverted at a *slight* angle (not enough that it protrudes from the side of the cowl at all) and have the muffler still pointing out the bottom of the plane. Granted, it is on one side of the bottom (not directly in the nice little tunnel that GP designed into this plane) but it should keep from needing to cut the cowling at all for either the cylinder or the muffler-- other than the usual opening on the bottom. I really want to keep the cowl attachment/removal from needing to remove the muffler every time!

I agree that the build so far has been pretty uneventful. I can say that I like the "pre-cut" CA hinges (as opposed to needing to cut them from a sheet myself... yeah, I know, I'm lazy! )