well according to O.S. .12cv specs shown on thier webpage, I estimate you should run about a 7-6" daimeter prop with 4-5" of pitch (7x4 or 6x5) the only thing I forsee as a slight problem is the manifolds for those engines.i might look a bit wierd having the tuned pipe out infront of the engine mount, but it'll work. The torq .16 is from duratrax right? I asume you got the O.S. to replace it? If this is your first Airboat, I would reccomend using your OLD engine first, as airboats are prone to tipping over and getting the engine wet. but that is up to you.