Just a wild guess....Consider that HUGE carb hanging on one side, and the LARGE muffler on the other, then the narrow cowl, I would say "get out the Dremel...." If they could come up with a design that had a more reasonable sized carb the engines would fit more planes neatly.. I think you can go to Zenoah web site and get the measurements for the motor, then get the manual for the Cub and compare measurements with the comprable glow engine. Cliff