and like I said, not unique to 75's either - my 71 has 'em.. and I remember at least one Scamp I had that I used those holes to mount fog lights.. it's like the tabs with holes at the front of the radiator support (not all cars) - WTH are those for!?
No doubt there are extra holes. :D But was anything ever attached on your bumper? If there were lights on mine, you would think there would be some remains of wiring, switch, something...