If the crease area still needs some work, I would find or make a piece of steel that is a good fit into the crease from the front. This should be 3 to 4 inches wide, made from plate 1/8- to 3/16-inch thickness to offer the part adequate support. (Hint: A brick-cutting chisel may be good for this!) Hold this tool in a vise with the "business end" pointing straight up. Now you can carefully position your grille bar over this tool, so the tip of the tool is nestled exactly in the center of the groove, and carefully tap any high (when seen from the back) areas down with a hammer, until the air gap is gone.
The finishing step is to carefully file or sand the face of the bar to reveal any minute low spots, and work these up with careful hammering. When all the low spots are removed, the part will be ready for repolishing!