I pulled the bumper off a truck once...It didn't make a sound...just felt a little tug and nothing but bumper laying on the ground, dragging behind the recovery truck. Thankfully, it was before cell phones...so no video!
That entire front plate that is still on the XJ isn't stock, it was part of the bumper. The flat plate is bolted or welded to the unibody. I think a stock XJ has little tabs and holes in the front panel.