The holes could be a byproduct of the panic button craze. I had mine screwed to the dash of my '74 Charger. Whatever went in those holes wasn't factory or dealer installed.
1) I doubt someone whould have gone to the trouble to neatly punch a rectangular hole in the dash for such an item, nor does that explain the dash lamp behind it.
2) the vehicle does have dealer installed cruise control, something else could have been installed at the same or added at a later date.
I just retired from the autotrade after 25 years in the field, installing options on used cars that are a few years old is very common.