Every glow engine in captivity is imbalanced, some worse than others, but all of them are out of balance. None of the crankshaft counterweights are sufficiently heavy to balance out the weight of the piston, pin, and connecting rod. So, what is balancing a propeller accomplishing? I think not very much. I think balancing propellers makes sure that we won't make the shivers worse no matter how we mount it on an engine. I suggest using a propeller balancer to find the heavy blade and stick that one on the same side of the crankshaft as the counterweight to help balance the engine. Make the imbalance work in your favor. Of course electric motors are balanced and a balanced prop makes an e-power airplane run even more smoothly.