My 15.5 lb 1/4 scale J3 flies nicely with a 26cc 2 stroke gasser. A little more than scale power, nothing close to unlimited vertical but I don't have to cut loops unreasonably short at the top. A suitable gas converted 4 stroke single might be something like a Saito 220 (36cc). With glow or gas I add 50% to the recommended 2 stroke to size for 4 strokes. My 220 is slated to power my 1/4 scale Taylorcraft Clipped Wing when I get it running right. Similar weight to the Cub.

If that Husky ends up weighing 19-20 lb I would be looking for a bigger engine than an OS 160 twin, even on methanol. That's just me though.