I run 2 340 cc Xenoah engines on my Airboat. They are 2 cycle, if your max horsepower is around 6800 RPMs then you can use a 2.6 to 1 reduction drive I bought mine from J Bird, They mainly deal with small aircraft stuff . The Reduction Drive ratio mainly depends on what RPMs your Max Horsepower is. If you need any more info as far as J Birds phone #, let me know, Thanks Dave.