The TT Pro 46 will balance the Kadet better than the 40. With the 46 you wont need as much nose weight to bring it into balance. That's what we put on my g/f's Kadet. Now believe it or not, I put a TT Gp 42 on a Kadet Senior that I built, and it flew fine. I had to add more weight to get it to balance, but it flew OK. Now I would rather have had more engine. I learned on that combo, it could fly real slow. I still have it and it's flyable. Both engines you describe are good engines. The extra power will really make a difference though. One thing I noticed with my TT Gp 42 was that I had to be sure I was getting full power in order to take off from the grass field I fly at. Once in the air I could throttle back and just cruise around very nicely. If you have a TT Pro 46, use it on the Kadet, it's good engine.