Take a look at the OS 91FX. It will drop right in without mods, weighs the same as your .61, is much more powerful, costs about $200, and pulls my Delta Fighter along at 127 MPH confirmed with radar. I use a 12X8 APC prop, a Performance Specialties Ultra Thrust muffler and 15% Cool Power fuel. I realize you won't get near that speed in a boat but it will wake it up in a hurry. It's hard to beat the OS91FX and I own several Jett engines.