What's the chances of a set of louvres from an older (eg: 1996) Pontiac GTP to cool the engine bay. I think they'd look allright placed right where they are on the GTPs, but would they vent some heat at all? Would it be a noticable decrease? color-keyed to your car, they'd be less noticable than the black (non-functional) louvres on the Z/28 hood...

 

The 80/81 Z28's had vents in the fenders. Can't check it when I'm going down the road, but when my 81Z is sitting in the driveway running I can feel warm air coming out of the vents. I'd say any decrease in under hood temps is a good thing. These 3rd gen cars run way hotter than the earlier ones and it can't be good or all the plastic parts, the transmission fluid, oil, etc.