If mine where anything to go by, i think people left them off after removing and replacing the rear bumper because they make refitting it a nightmare. I managed to do mine on my own but if it comes off again im deffinitly getting a mate round to help.
if you look the bumper mounts and the splash pans have to be fitted to the bumper then it all needs to be offered up to the bus. Its quite heavy and awkward and if youve just had your bumper powder coated...........well im sure you can imagine.