How to remove top cover of Cluster Box?

Mixtile Blade 3 (Mixtile Cluster Box)
#1

For a modification I’d like to access to the top of the cage accomodating the nodes and backplane, So I need to remove the top cover of the case of the Cluster Box. Removing the 8 screws on the sides of the case, two screws fixing the rail of the control board to the inside of the top cover, and two screws on the upper part of the cage does not help, as apparently the front part of the top cover is somehow fixed to the side parts of the cage.

What do I have to do in order to get the top cover removed?

#2

Apologize for the late reply. The top cover is permanently attached via rivets to the central chassis frame and cannot be removed.​ ​Please pursue alternative access methods for your modification.