The reduction gear adds complexity and weight (8kg?), you can not handprop the engine. The Carden-Ford had 65kg, the G13 is 53kg bare engine. With 40 HP you do not need large propeller (propeller fitted to 'ESZ is 40" x 30"), so you save another weight and the wingtip speed goes down, no problems with prop noise at all.... the AM10 run at just 50% power would still provide about 38 hp, substantially more power for less weight than the Chilton's original 31 hp Carden-Ford. The result would be a very smooth and quiet engine with the prop turning at just 1200 rpm (more if you change the reduction gear ratio). Why would that be a bad thing?