If it were a 1/4 elliptical, then the radius arm bracket would be attached there.... I think.
If it is on the left side of the car, it's for the exhaust pipe hanger. Hanger bolts in there and the clamp on the bottom goes around the exhaust pipe.
Okay. You just sent me diving into the wheel wells of my '69 Mark IV: I've got the same holes on my car and there is absolutely nothing hooked up to them. I don't have a sway bar on my car (yet), so I can't confirm or deny these are sway bar mounts. Either that, or we're both missing something!
Don't forget that these cars changed very little over the years - I have found a number of "leftovers" from previous years that it just didn't make economic sense for them to change. Sometimes it is obvious, like the transmission plug holes in the shell not matching the 1500 transmission. Others are things like various pieces of the wire harness that just went by the wayside - but are still included in later cars. So, there is every chance this goes back to the 1/4 elliptical - and they just never changed it.