NGC or GPEC2?

Guess it depends on what you want it to do. GPEC allowed for more integration and features, among other things that do and do not have to do with running the engine and trans. As for your AC issue, why not get away from computer controlled lsd's and just revert it to a manually controlled, clutch cycling switched system? I'm all for conversions, but with a lot of this stuff it can be pretty tricky if you aren't going to incorporate the whole system. In those cases, I would try to keep it as simple as possible.