Adding the 660ti's device ID to NVDAGK100Hal.kext clearly isn't necessary to get it to work, but someone mentioned earlier in the thread that it did bring back proper pci info in system information (instead of the clearly incorrect "This computer doesn't contain any PCI cards.").
So I'm looking at editing this section:
<key>IOPCIPrimaryMatch</key>
<string>
0x0fc010de&0xffc0ffff
0x118010de&0xffc0ffff
0x11c010de&0xffc0ffff
</string>
If I've got my conversions right these represent the following decimal numbers:
0x0fc0 is 4032
0x1180 is 4480
0x11c0 is 4544
0xffc0 is 65472
And it's said that there is no need to add a specific device ID because these are ranges, 4032 to 65472. But if that's the case here then why bother adding the second and third line, since those 4480 and 4544 are both within that range?
So I'm about to add gtx 660 ti Device ID: 0x1183, which is 4483 as a 4th line:
0x118310de&0xffc0ffff
Well that went badly. Refused to boot. Had to update me secondary ML install to 10.8.2 and install nvidia drivers, then copy the NVDAGK100Hal.kext from that over. Working now, but looking at the plist in the kext now it does even have the IOPCIPrimaryMatch key! Leaves me wondering if I had an old version, or if I'd patched it with multibeast and that had changed it...
PS the calculator.app that comes with the OS has a handy conversion feature between hex and decimal.