Its been done by a member in Sydney, not around much anymore, his name was Zul.
I have an AWD HNU12 rear end that a fellow member on here has purchased from me (Bloodstained) and he is fitting it to his currently FWD KA24DE which is already turbo charged
... so it will be an AWD KA24DE-T U12.
The fuel tank has to become a fuel cell in the boot or find an AWD tank (difficult). Otherwise the locating points for the AWD rear end have to be fitted/welded on. I believe some match up to the FWD stock and some do not. Not having ever done it, I'm not certain, just remembering what people have told me in the past.
The exhaust also has to be relocated on a FWD as it runs exactly where the output to rear diff runs, the AWD's has a lump under the front left of the drivers seat because of this (the cat convertor sits off to the side, under the driver, or passenger in the US).
2x engine mount points are identical, 3x are different and there is no north south cross-member like on the FWD's, there is an east/west cross member that runs across behind the radiator across the front of the car.
Thats about all I can think of right now!