Well, I'm a 4-stroke guy! Nothing sounds better than a 4-stroke. I have seen a lot of Cubs at the field and I don't think I've seen one with a 2-stroke. Most have been OS 70's and 1.20's (depending on the scale). I am building a GP J3 Cub and have mounted a OS 70 on it. True, even the GP instructions are "thin" when it comes to detailing the 4-stroke install. But then again, thats the whole art behind building. Filling in the gray areas!! I'm sure with help from the guys here you can do it and feel pretty proud when it flies. I vote for the 4-stroke.