Just an update...
Yesterday I tried to install Mountain Lion and it worked as well, I used the new UniBeast to create the USB install disk, than Mutibeast and the same DSDT.aml provided in this thread. At first had problem with sleep, It worked fine on my install test disk, it's an old PATA HD, but when I tried on my regular SATA HD sleep didn't trigger. Like Lion the drive icon show as external diskk (orange colour) but than sleep worked fine, to solve this problem i installed with Multibeast the IOAHCIBlockStorageInjector.kext that solved sleep and the disk show as internal.
A note on sleep, once in a while (months) it stop working, to solve it I need to fix permission and rebuilt system kext cache, for that I use Kext Wizzard but in the past OSX86Tools worked fine too, I have to say that I had this problem with all the OSX install method I used
Ciao
Davide