The 52 would probably work, but the 70 will work better. As others have said, the extra power will help for both this plane and other planes you may decide to put the engine in. The weight won't be an issue for a 40 sized trainer, they have a large wing area.

Something to keep in mind for winter flying. Be careful of your fingers when tuning the engine. There's the obvious problem of accidental contact with a moving prop. Don't forget the not so obvious problem of frostbite. One person here (on RCU, not in North Carolina) said he stopped flying in the winter because he got frostbite on his fingers while tuning his engine. The extra wind from the prop makes for a significant wind chill.