My first airplane was (and still is) an Eagle 2 ARF with an OS 46LA on it. I'm thinking that the 65 4 stroke is a little much. Even if you keep it throttled back to control airspeed, you may have so much thrust even at idle that the airplane will never want to land. You may also find you'll need a larger diameter prop to "absorb" the thrust from the engine. Too big a prop will cause a problem trying to taxi/land. You won't have much c;earance between the prop tip and the ground. You may end up breaking a lot of props.

When you say the mount is broken, are you talking about the mounting lugs on the motor or the wooden plate the engine bolts onto and which is glued to the wooden beams on either side of the nose?