RE: Is this enough engine cooling?
BTW, one very easy way to block the offside opening would be to use screen. It's easy to fit, and easy to epoxy to the back of an opening like that.
The screen will allow air to enter, but once the other, unrestricted opening starts to flow, the screen-blocked side will be virtually closed.
However, whatever you do, if you do not block the areas inside a cowling that's got a lot of open area inside, the engine is not going to be cooled by the airflow through that cowl. Since hot air is harder to move, the entering air simply follows the other cool air that's nowhere near the engine, the cool air that's passing out the holes at the rear and that also never came near the engine.