Leroy,

I am going to add another dimension to consider. What weight to you need in the nose to obtain a good cg? My 1/4 scale L4 (Nosen) was a beast at 22#, but a very fun friendly flyer. I had a Quadra 42 in the nose that gave a surplus of power, but also provided needed weight up front. In full scale the Super Cub carries a lot more power than the J3, so something that will swing an 18x10 prop smartly would be a good choice (though I will bet you will need lead in the nose for balance). In my book at least.

Have fun with it!

Bedford