I used one of these hot swap caddies by Lian-Li...
http://www.frozencpu.com/products/1...age_-_Quadruple_35_Drives_-_Silver.html#blank
I stripped away the fan, the door, and 5.2in mounting bracket and made four 2.5in long aluminum standoffs to mount to the bottom of the case and raise the cage high enough to clear the bottom edge of the G5 case opening.
Here's what mine looks like at the moment. Please excuse the ugly cable management (or lack there of), I'm still working on that!
My current HDD cage placement ensures some good airflow through the HDDs and on to the CPU. It also allows space above it for a second cage at a later stage, should I ever need 6-8 drives. The open space below the cage (thanks to the standoffs) also allows for some airflow to reach the CPU and is a nice place to hide a few cables too.
As you can see, my mod was done with expansion in mind. There's ample room for another HDD cage, an ATX mobo (I currently use a mATX board), more graphics cards and a better CPU cooling solution.
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