Remember,
The GTOs were designed to go 175 mph, so everything was streamlined. They put doors, or flaps, on the cooling intakes with flush buttons to open. Airplanes use these buttons on the engine inspection lids.
I was thinking about not actually cutting the radiator cap door on the hood (or wherever.) Just reinforce the glass under the area, then carefully grind a shallow channel to simulate the door. These are replicas, right? It doesn't have to actually be exactly the same, especially if you leave out some things like pushbutton door pulls, perspex air scoops on hood & back window, the aluminum 5-speed shift gate....
But I think we can have some fun over the (idle) winter month coming to throw around ideas.