People do seem to bolt the VW boxes to quite a few engines, so that might be an option. The only thing with the VAG 4WD system is that it's Haldex, so only part time 4WD. It would make for good traction, but wouldn't be any good for donuts or any of that business (if that's what you're in to of course). I'm not sure what kind of electronics would be required to run a Haldex system either, so that might add some complexity.

I'll certainly be interested to see what you choose, but I am way too lazy to do that much work