The Camaro spoiler wasn't designed to direct airflow to the radiator, it was for downforce.

If you need more air into the radiator, I suggest the factory lower baffle pan that was used on the Firebird 400 cars, and the two upper baffle panels that go between the core support and the front bumper panel. These 3 pieces are all reproduced now in steel (you may be able to still find the fiberglass versions if you're not concerned with numbers matching), and they will force more air into the radiator that comes through the valence panel and grilles.