I believe you are talking about the "Big Swamp Buggy" right? If so, yes you can put a .61 engine on it, but you had better be good at getting the balance perfect(boat to run level) as this boat set up right will fly. Mine with an O.S.61VR(20 yrs ago) actually made it to about 6 feet in altitude before it remembered it was an airboat not an airplane. Did not do too much damage. Dennis