I built the firewall as per instructions because it is more than strong enough. I am using the stock muffler witht the engine mounted horizontal which made using the stock muffler impossible unless I made a large relief in th bottom of the fire wall which I did. The muffler did not protude beyond the bottom of the cowl so I am going to have to come up with some extention or use a different muffler but money is tight right now so I will have to make do with the homemade extention.
I called Horizon and they said as long as I am not looking for outlandish 3D stuff the Saito on 30% fuel with a 16/8 the plane will fly just fine. They had the same motor on a 13.5 lb Ultra Stick and on the fuel and prop set up it would pull away from a hover. I plane on flying mine this weekend so I will let you know how it comes out.