A 2x4 might split. It would be OK for checking the CG movement, but I wouldn't fly it that way. Better to use aircraft plywood stacked up. It only needs to be stacked at the mount bolts. Cut 1x1 squares of 1/4in. plywood and drill them. Also 2in. out might be too much. You are moving a lot of weight when you move the motor. What is the chord of the wing? I have an 83in. World Models Super Stunts 60(Stik type plane). I am using a glow GMS .75 that is set out 1/4in. plus the battery is behind the fuel tank and 2oz. of lead on the cheek cowl. The big wide stab. and short nose on the fuse cause the need for weight. It is still a floater.