You have some good questions regarding the side thrust. During the design phase and flight testing I found that the plane did not need any side thrust for the engine. The forward bulkhead has down thrust built into the design so that will not be an issue. Regarding the exhaust system you can see that I use a tuned pipe on mine with no ill effect to the anhedral stabilizer. You should not either.

You will find that due to the design of the fuselage it will fly straight and true even in a knife edge and breaks clean in a verticle stall. The plane is easy to fly and is very fast at full throttle you will be surprized how slow it will fly and land. I would recommend you add a 1/64th plywood doubler to each the side of tail area inside the fuselage to add strength to the tail. make it about 12 inches long. It will add support to the tail and also help with the balance since the plane has a minor tendency to be nose heavy. The additional weight (which is miner) will help it's spin carateristics and improve the landing.