I agree with the antennae....if it were a spotlight, it would have gone through the inner ceiling as well.
A roof spotlight was pretty common on farm trucks around here in the mid 60s. It was a pretty good way to check on irrigation, animals, etc, at night. Lots of fun for a kid, too. One could play spaceship, submarine, cops and robbers, almost anything while hanging on to the handle and rotating the beam up and down and aroound.
Don't guess the safety folks were too keen on having a metal handle hanging down in the middle of the truck...
