The props are what is going to be the hurtle here. I'm going to start out with a 14.5X14.5 and trim the dia. until I get the desires rpm. The Macchi has already flown with as small as a 9" prop. I can see a 11.5 X 14.5 working. Would be worthless for racing but may work for a speed dash. The speed dash airplanes are subject to the same rules correct? We don't want some guy showing up with an FAI job and posting 220 mph. Perhaps requiring it to be the same airplane you had raced with?