Bjorn, I did find the video of the Bird in Question in Kelly's video file.
http://www.youtube.com/watch?v=YQCNYBTNI6k&list=UU3oTwJFIAiGIxTXnjOnjd3g&index=4 Go to about 1 minute and there is some good side shots. It is the red 68 Vert in front of a red 69 Vert with Buick wheels and bald rear tires.
It looks like a Z-28 style being more angular than the T/A style and also looks as out of proportion as a TA one. If I were doing this, I would section the scoop a bit shorter and narrower to make it fit and look better on your 68 Fenders.

Another thought, how about cutting a hole(s) in the firewall into the cowl area to relieve the pressure. The air would then go out over the windshield and to the rear spoiler and relieve the air build up in the engine compartment.