Red,
The counter balance has to balance one half of the weight of the piston,rings,con rod and wrist pin etc. It is easier to do on a your engine, because you can weigh the piston and rod assembly sepparatly with a gram scale. Use a prop balancer, such as Hi-Point or Topflite after removing the crank shaft from the case. Attach a weight to the crank pin equal to 1/2 the weight of the piston assembly as stated above. Carefully remove material from the counter weight until it balances. If the crank pin side is the heavy side, you will either have to remove some material from the piston or rod or add weight to the counter weight. This is more difficult. Drill holes in the counter weight and press in a heavy metal such as tunstun or lead. All holes for adding weight should be paraell to the shaft. Since the cutdown flywheel is keyed, weight can be added to it, being careful to not weaken it. Let us know how it works out. Good luck.

Dave