I'd like to add that I update to 10.8.3 using an install from your guide with success.
Here are my specs:
Gigabyte Z77x UP4 TH
MSI nVidia GTX 670
OCZ Vector 256GB
Seagate 2TB
16GB RAM
I just updated my system using App Store update then reinstall Audio Kext since the update overwrites the audio drivers.
Note: I had to change my system definition from MacBook Pro 8,1 to Mac Pro 5,1. Using the MBP definition crashes the system when viewing videos by Quicklook which is annoying. Once you hit the space bar on a video file, Quicklook starts to show distorted magenta images. At this point, the system just freezes. I also had to remove AppleTyMCEDriver.kext from /System/Library/Extensions as this kext causes KP on boot when using the MacPro 5,1 definition.
Sources:
http://www.tonymacx86.com/graphics/...g-quick-look-function-finder-video-files.html
http://www.projectosx.com/forum/index.php?showtopic=102 says:
"Nehalem ECC RAM support, could be used for more, will have to explore more. Problem with SMBIOS's identifying model as MacPro4,1, if so then make sure to delete AppleTyMCEDriver.kext, not needed for 90% of systems anyway."