Step 2.  Machine the Rear Panel

The layout of the rear panel is not at all critical and you can machine it however you like.  The drawing below shows one possible layout for the rear panel.  This layout is based on the DRO-350 rear panel so if you already have a DRO-350 case with the original layout, then you can just add the extra connector holes that you need.  Just be careful to stay away from the standoffs that are on the inside.

DRO-550 Rear Panel Drawing (Click for PDF)