You didn't say whether this isa tail dragger or trike gear. If it is a tail dragger, put the main gear just a little in front of the CG. If you get it to far forward, it will be more difficult to take off and will tend to bounce on landings, to far aft and you will be constantly nosing over durring taxi. If it is a trike gear, put the main gear just slightly aft of the CG, to far aft and you won't be able to rotate for takeoff without excessive ground speed. Also, on trike gear, keep the amount of movement on the nose wheel to a minimum, not more than 10 degrees left or right.