Hard boiled eggs and nuts.
It appears to me that there is no "transparent" glass in the windshield. Could they have been working for the State Department? LOL!
My guess is that since they seemed to have wrecked virtually every car they ever drove, the producers took the safe route and removed the glass. Wonder how many of us noticed that "back then" when we watched this?
That plus the light reflection issue. I've had a car on a set before. They get really uptight about any reflections showing.
That's a process shot. The Boys are on a studio set with the background projected behind them. I think another reason a lot of their cars have the windshield removed is to give the camera an unobstructed shot at them.
It is a process shot and the glass was almost always removed for the reasons mentioned above. Mostly reflections when filming.