Dont know where the CG would be, but you balance a low wing plane upside down. If you dont have one of those balancing stands (Great Planes or whoever) you can make one out of pine and dowels. Hell, you can use your fingertips for a rough estimate.
To balance a plane laterally, you need to hold it at the tip of the spinner and the very rear of the tail as close to the thrustline as you can. Whichever wing drops, add weight to the opposite.