That's some good info Rusty.
The chrome bumpers I pulled off of an original '72 Explorer, I thought, both had the holes. It's been awhile, and I've long since adiosed them both I think. But I was pretty sure I bought short carriage bolts to fill the bumperette holes on both bumpers.
To the best of my knowledge, the bumpers were original to the truck, unless any of them had been replaced for whatever reason before my friend bought it from the original owner when it was 2 years old.
So to confirm (and just wanting to see some of the old pics again

), I've been staring at some old pics from a Rubicon trip in '75 that show the truck. I'd forgotten that it actually had the front bumperettes! Cool.
In one pic I'm sure I can see bolt heads in the face of the rear. Had to use a magnifier, but I'm sure they're there.
Paul