Hi Carver--I've built the 4* 40 and a couple of 60's. The fire wall is installed with the correct thrust angle. Just use the template that comes with the kit to lay out the motor mount. The kit comes with Sig's 2 piece motor mount. I like to temporarily install engine to mount beams using small sheet metal screws, then attach to fire wall to get the holes correct. Then you can slide the engine in/out as requried for proper CG and looks. As I recall, you can move the engine around about an inch. Makes a big difference in CG and may prevent adding useless weight.

Good luck-let us know how it flies.

Greg