Louvers are not usually put in the back half of the hood as there’s high outside pressure there which would cause the louvers to add undesirable under-hood pressure.

I do want to shed some heat from manifold, turbo and downpipe though.

At one point, Singular Motorsport put about a 1” upright at the front of their excellent front-half louvers. If I did that with a far-back louver, would there be enough turbulence created to make airflow suck air out of the louver and to allow hot air to rise out of it?

 

Nope. Pressure is too high from windshield.

Best bet is to duct the radiator as much as possible.