The pass side has two "L" shaped brackets that bolt across the top of the standard welded in seat skirt. They provide the mounting point for the bottom of the pass side seat back. The top hangs on brackets that bolt to the back of the cab. The driver's side seat bolts into the bottom of the cab in holes that you drill where there are already marking spot indentions if that makes sense to you. They also bolt to holes that are already in the front to the seat skirt. As you mentioned, the filler plate screws to the seat skirt and fills the gap below the seat adjuster. I think I probably have pictures to make it more clear if you want to send an e-mail address in a private message.