First of all sorry for my bad english, but I think I can help. I also have a optiplex380 and know your problem. with me now mountain lion runs without problems . ..."sill waiting for root device"... is your fault.If you want to googling yourself. At boot screen typing -F, -v and it boot, but that "not always". After much back and forth 1000's kext i am now back to vanilla kext´s
Finally:
Only the org.chameleon.Boot.plist and smbios.plist in extra folder i adapt and it boots without problems. PS: a kext for the lan card is also available
MY smbios:<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>SMbiosdate</key>
<string>02/29/08</string>
<key>SMbiosvendor</key>
<string>Apple Computer, Inc.</string>
<key>SMbiosversion</key>
<string>MP31.88Z.006C.B05.0802291410</string>
<key>SMboardproduct</key>
<string>Mac-F42C88C8</string>
<key>SMfamily</key>
<string>Mac Pro</string>
<key>SMmanufacturer</key>
<string>Apple Computer, Inc.</string>
<key>SMproductname</key>
<string>MacPro3,1</string>
<key>SMserial</key>
<string>.....................</string> -------- your own SMserial
<key>SMsystemversion</key>
<string>1.0</string>
</dict>
</plist>
MY boot.plist:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>EthernetBuiltIn</key>
<string>Yes</string>
<key>GenerateCStates</key>
<string>Yes</string>
<key>GeneratePStates</key>
<string>Yes</string>
<key>Graphics Mode</key>
<string>1024x768x32</string> -------- your own for your Panel
<key>GraphicsEnabler</key>
<string>Yes</string>
<key>Kernel</key>
<string>mach_kernel</string>
<key>SMBIOS</key>
<string>/Extra/smbios.plist</string>
<key>Timeout</key>
<string>2</string>
</dict>
</plist>
hope it helps