Some years ago, I flew "your" cub on a tired OS .30 2 stroke. It flew just as you would want a cub to fly and was still a touch overpowered. That one was covered with Monocote. Later, I built theclipped wing version, covered with Super Coverite and painted as the Hazel Sig CW. That one was powered with a KB 40, 10X6 prop, which turned out to be too much torque. Changed to a 10X4 prop and it was just right, flew like an aerobatic cub. Both engines you have will fly this plane fine, and the 4 stroke will give the nicer sound. It's a win-win choice you have.