I say some sort of gray, charcoal gray to be specific, maybe even with some metallic in it, then give them a red and white stripe job around the outer edge. If you have any of the old Ford truck "crown" style caps (from your trucks era up to 79), I'd detail them up using the same color combo. I think if you do something too bright, it's gonna end up the focal point and will take away from your trucks cool look.
I can't wait to see your choice, I am a huge fan of 67-72 and 73-79 Ford trucks. Great looking truck!