You definately have to cut out the louvers. The instruction book that comes with the kit makes this clear. I also cut a good size opening in the bottom of the cowl. Normally overheating will make the engine sag. This could effect the flight characteristics if it get a surging action. I wouldn't thing the incidence being off would make the aircraft unstable, just a little hard to trim and difficult to get tracking properly.

On my first flight I used metal bolts in the plywood blocks to hold the wing on. I "zapped" the holes after tapping to harden them. I found out later that using metal bolts in tapped wood is a no-no. They vibrated loose partway through the first flight throwing the incidence off. It was a handfull let me tell you.

Barry