Current SPA rules allow a +/- 3% deviation from original plans. The airfoil could be thinned, but I don't think it would make much difference. My fuse was wood, so I just made the ventral fin from hard wood and mounted a tail wheel bracket. An interesting thing happened. With the first plane, there seemed to be an area as the tail came up or settled in where directional control was an issue. I started with fairly narrow main gear mounted to the fuse and swept back under the wing. It handled like a squirrel on speed. I eventually went to music wire out in the wing. I still had to hold the tail down during take off. The best I ever did was, unfortunately, not ended with a landing.

Pumped engines are OK in SPA. VP Tom Atkins has used a YS61 the last two years. The 63 would not be allowed because of the super charging. There is no prohibition against rear exhaust, just pipes. Tom, incidentally, used a dynathrust muffler.