Norco changes their builds every so often. My guess is that those top two big pieces in the upper left/middle are PSU plates. You need a different plate for ATX versus redundant PSUs since normal ATX power supply cutouts get in the way of hot swapping PSUs. Just a guess though.
I think you are right about the rectangular plates, you are going to be OK not using them.
I think you are right about the rectangular plates, you are going to be OK not using them.