BMathews has given you some excellent advice. I'll throw in my opinion for what it is worth. Your plane needs to go on a diet or get bigger. There's just no way around it.

You are proposing a very expensive power plant (x2). It would be a shame to destroy them on the first flight which will almost assuredly happen if you proceed. You need to decide if you are married to the size of the plane or the powerplant. If you want to keep your present power plant it needs to get bigger. If you want to keep the size then you should try to work out some sort of an option using a glow engine. I suspect it would be difficult to find a suitable gearbox to turn those big rotors, but you could probably get one made.

Good luck, this is a very ambitious prject. How do you intend to overcome the control issues during transition?