The 4120 is a little light for that plane. The AUW is 7 to 8 pounds. It flies OK, take-offs and landings are great, but the flat out speed is half that of glow. There is just nothing more when the prop unloads. You want at least 700 watts in the air. The Axi 4120/18 and 6 cells into a 13x6 will seem powerful on the ground, but you'd be lucky to get 300 watts in level flight.

There is no electric CG in the manual. Marking the CG with a full fuel tank before it is converted would be the best way. Which on this plane will put you 1/2 inch or so forward of the number in the book. BTW, for the B.H. models Extra 330 it 1-1/4 inches forward of the number in the book.