What goes here?

1973 Dart Sport. One of the front fenders must have been replaced, because the left side has these two holes right behind the bumper and the right side doesn't. I assume some sort of inner bumper cover went in there. Does anyone know for sure and/or have a pic of it? I'm considering pulling the bumper in a few inches which would eliminate the need for anything in there, but I'd sure like to know.

View attachment Fender holes.jpg