If you elect to replace the engine, give some consideration to the C-85 with the O-200 crank, pistons, connecting rods and carb. I used the STC from Aircraft Specialty Services and phone help from Don Swords. Everyone who has flown the Cub with this engine has had a WOW experience!
Google Don Swords at Don's Dream Machines. He is a real gentleman and will take the time to make you smart.
Don can also handle the STC.
My "free" C-85 had toasted crank, cam, cylinders and carb. It was missing the mags. So it was just some extra bucks to go the STC route. In retrospect, if I had a better case, it could have been done cheaper. But the C-85 with O-200 parts -ROCKS!
Pete