Help with Mountain Lion installation on USB - Wont boot internally I'm hoping you can help me out with a strange issue I've been dealing with the past few days.  I recently purchased a 2008 Xserve.  I've been trying to get Mountain Lion on it without much luck, however I'm very close.  I know mountain lion is not 'supported' on this platform, but there is no reason it won't run.  I've replaced my mezzanine video card with a mountain lion (and lion) supported gt 120 from a mac pro.  I've installed mountain lion to a 500gb drive via USB off of my macbook pro, and edited the PlatformSupport.plist file to contain the proper board id from my Xserve.

Here is where the issue is: If I try to boot to Mountain Lion off this drive via USB on the Xserve, it boots and runs mountain lion buttery smooth.  When I place this drive into the first drive bay (internally) in the Xserve, it wont boot.  Its as though it cannot find the drive or boot partition.  It sits at a white screen and I eventually get a blinking folder with a question mark on it.  I feel that I'm so very close to getting this to work, and its driving me crazy.  Anyone have any insight?

Additional Information: 


booting holding option or to the recovery partition while the drive is installed internally does not work either.
Installing Lion internally works fine, so I know its not a hardware issue.
I was able to get it to successfully boot by creating a Time Machine Backup, then restoring that to an internally formatted disk.