You can try
www.gizmomotors.com for modded motors in 26 or 29.5 cc's.
Forget the clutch, it's just more weight for a boat that's going to be heavy as it is unless you're running alone then you might want it for starting while it's floating.
Get an Easy-Start from Zenoah, Gizmo has those also and make starting an Zenoah a LOT easier.