Are you typing about the black pieces that fit inside the front fender wells (between the body and the metal going to the subframe?) These are bolted into place, and they should be painted to match the body. So they would have gone in first, then the inner fender sprayed.
On my 280 SL they are held in place by six bolts/washers. Not sure what the bolts screw into.
I am sure someone will chime in.