I want to say lower radiator bracket [passenger side] mounting point - because I snapped a bolt off inside of mine (and haven't drilled it out yet... so yes, that means the lower passenger side of my radiator is technically unsecure).
Correct lower radiator support bracket. Only the outside one is used on each side. I think the interior threaded hole was for another application possibly Cougar.
You should have the same thing on the upper part of the radiator support for the two radiator clamps on the top. There was a wide radiator and a narrow. I think 6 cylinder some 302 and non air 351 had the narrow.