No such thing as overpowered. I had a 52 inch span plane, and the recommended size was a 30, So it had trouble taking off on grass (had to be on full throttle, plus a long run), so I put in a 45 and wow it took off with less throttle, and in a lot shorter distance too (it flew great). My Lt-40 has got a 70 span, so I fitted a 61 (not the recommended 46). Since your plane fly's great with less throttle, just use less throttle on takeoff (since your engine is bigger), So don't worry (though if you want, you could fit a 61 size engine)