In theory, the 69 and up hoods are less aerodynamic, forcing the flow of air to separate from the body. Basically, meaning it bounces off the hood's leading edge, and falls back near the cowl. In the pages I have down on this post,
page/image A4-fig.16, bottom left corner illustrates this well.
Read your hearts out: Loads of stuff about front-end design on boxy things.
Aero development on the VW Rabbit, loads of info of how the design of the nose effects air flow.
A1:
http://i42.photobucket.com/albums/e3...ROFILES/A1.jpg
A2:
http://i42.photobucket.com/albums/e3...ROFILES/A2.jpg
A3:
http://i42.photobucket.com/albums/e3...ROFILES/A3.jpg
A4:
http://i42.photobucket.com/albums/e3...ROFILES/A4.jpg
A5:
http://i42.photobucket.com/albums/e3...ROFILES/A5.jpg
A6:
http://i42.photobucket.com/albums/e3...ROFILES/a6.jpg
Air flow on box-shaped vehicles
B1:
http://i42.photobucket.com/albums/e3...ROFILES/b1.jpg
B2:
http://i42.photobucket.com/albums/e3...ROFILES/b2.jpg