Thanks, William! I'd love to see that article.
My 68 is front spoiler only. I had never thought about it, but the front end does stay where it is supposed to be when I drive interstate speeds. I guess now I know why...
joesaur,
Back to the first part of your original question: Running at 70 mph, with the factory AC on in 90 degree plus weather ,for five hours to Beckley, WV (in the mountains), it did not overheat. However, I still think the cooling from the spoiler is minimal, and I do not have all the seals mentioned for air conditioning in the 68 AIM at C60, B3. Never found seal 3937188. The seals would force more of the outside air over the radiator.