I would calculate the CG myself. Don't trust the manual. Should be able to start at about 25-30% of the chord on a straight wing. You can also set the motor out some to offset adding so much weight. Moving the motor(2-3lbs.) out a half inch will make a difference in the weight needed to balance it. The two servos in the tail are at least 3oz. that need to be offset by more than that at the nose.