I decided the best thing would be to buy more compatible hardware so after a bit of research swapped out my existing setup for a Gigabyte GA-Z77-DS3H.. not only is it very compatible with Mountain Lion, it's also quite well priced and more than suits my needs. It was also a convenient time to move up from a Core 2 Quad to a Core i5 CPU..
I just spent the evening deploying Mountain Lion using the Unibeast / Multibeast method and couldn't be happier. Only had to do minimal tweaking (setting PCIRootUID=0 to actually get the installer up) and everything seems to be working as far as I can tell - though I haven't tried sleep / suspend or anything like that yet. Sound / LAN / video all seem fine.
I've done the build on a spare harddrive I had lying around - next need to experiment on deploying it to my normal boot drive and setting up Chameleon to boot Windows too... as I still want to play Battlefield 3!







