Thanks to this adapter plate that replaces the original optical and disk bay for the HP ProDesk 600 G3 you can mount up to 6 disks while still being able to mount the top enclosure of the PC.
The model for the disk bay is: 3 Slot 2.5" HD SSD Bay by Ciro Lucio Tecce | Download free STL model | Printables.com that enables to host up to 3 disks per piece.
The adapter plate fits in the original PC structure and it's held in place with a peg to be glued on the main part.
The disk bays can be glued with the adapter plate and mounted as a solid piece.
The author marked this model as their own original creation.