My non-original hood is raised like a cowl induction hood, but actually theres no air-flow from the back of the hood into the engine bay. The area behind the raised part of the hood is closed up with a metal plate. I was thinking of cutting that metal plate out of there and possibly putting in a piece of screen to keep out leaves and stuff. Anyone have the same kind of hood and try this? It obviously wouldn't be as good as a real Chevlle Cowl induction setup since the air cleaner would not be sealed from the engine bay air, but it might at least help keep the bay a little cooler. Any thoughts?

I saw a 70 Chevelle in Chicago 2 weeks ago that had that done to it. You might be able to make up some sort of sealed air cleaner for it.
Heck, it might even work better than the factory cowl induction as they weren't really that efficient.

My car was modified similarly by the original owner on "Day 2". He removed the rear panel, added a lower panel similar to that used with the CI hood, and a Corvette L88 AC with the small big screen top which was used with the open element base. I returned it to original though. I agree with the above, if sealed, it will work as well as the CI by providing cool outside air. The flapper is just a gimic. You don't see them on real race cars that had/have cowl inlet. Also note the factory offered over the counter cowl inlet air cleaners where they cut through the fire wall in to the cowl air plenum with out any mods to the hood!