It's a great idea, in theory. But I don't think you could use the AWD tranny from the Skyline. Instead you would need a tranny from say a Porsche AWD, so that you would have the right power distribution. Then you would need to make a new Chassis for the car, and mount the body to that. And the amount of fabrication needed to make that work on a s30 or 31 uni-body is obscene. Then you would need to add ballast to the car for better weight distribution. And on & on & on.
Lets make this simpler get a Porsche with AWD. Cut of the body, mount an RB26DETT. And slap a Z shell on that. Viola a rear engine AWD, RB powered Z. Well sort of?