Mike
If you mean the rounded brackets, they are for taking the ball of the large GHE rubber fasteners that were fitted when a ducktail was put on the car later in its life, as mentioned in the post they used fronts which have the rounded ball fastening unlike the original small GHE rears which have a straight "T" piece.
I plan to have the holes in the bumpers welded up again because I am pretty sure that is how they left the factory.
Tim