If it was not so darned cold, I would go out and try a monster prop. right now. I know a lot of people say not to plug up exhaust and over prop, but as long as they don't overheat or detonate, it is worth a try. It may require a few shims in the head. I read an article on a Fox .35 that welded a cylinder onto the opposite side of the case, and plugged the exhaust, and carb to get it slow enough for the plane, and it worked good enough, I think the guy in the article said it lasted well and putt putted away.