RE: Senior Ailerons and Engine
I can't speak to the aileron effectiveness vs. the dihedral in the kit, but I can tell you the ailerons work very well on the ARF version. You might consider using it as a guide. If you're interested, I can take some measurements and or pictures if you don't have access one of the ARFs.
I also have an O.S. .70 4-Stroke on mine, mounted horizontally with a slimline pitts muffler and turning an APC 13x6 prop. Everyone has their own opinions on power-to-weight, but I think the .70 is a perfect match for the senior. Mine comes out of the water very easily with properly set up floats.