The PO mounted the Pelicans, and all the other farkles. They're easy enough to remove, you just unscrew (by hand) two knob bolts inside each case and they come off. Open the case, hand-turn the two big knob-bolts (large bolts with knob handles). Each case has two knob bolts that screw all the way through the rack mounts.
The cases rest on a mount that's attached to the outside of the case and rests on the lower rack bar (the mount is screwed to the back of the cases, rests on the rack bar). All of the weight of the case rests on the lower mount, which simply sits on the rack bar (not attached to it). The top knob handles, screwed through the case into the rack, hold the case to the rack.
Does that make sense? If not, I can post pix.