Open cowl vents?

[BC12D-4-85]

https://fadodge.com/winter-front/

Customary and traditional for Pipers with front mount. Can be drilled to allow some flow. Can have moveable block off plate added behind that's adjustable - slides sideways to open or close holes. Can have cockpit cable to move plate. Had one on two PA-18's. Good from -50F to +50F.

Gary

 

[mvivion]

Similar thing is STCd for Husky with rear mount cooler. Probably could be FA on Cub with rear mounted cooler as well.
MTV

 

[rv6ator]