Haha, I actually just signed up yesterday and stumbled across this. Looking for info on building an NA 2jz or vq35 swapped 240z when saw your post. Keep in mind cobb that with the way the RB26's awd system is setup and the overall size and weight of the motor (iron block twin turbo + 6 speed manual with transfer case) would mean that should it happen to fit in the front of the car it will be even more nose heavy to begin with.
I'd start out first by measuring two things. First off the overall length of your engine bay from firewall to radiator, and then measure the distance from the center of the wheels to the radiator.
These two measurements will be critical because right now your engine is really only 2 cylinders long longitudinally as opposed to 6, so although the RB only has 2 additional cylinders, it's going to be 4 cylinders longer than your EJ. The other measurement is important because the transfer case and driveshafts for the skyline run through the oil pan dictating the placement of the engine based upon the front driveshafts. This means no moving it forward or backward to any great degree without fubaring the angles of the front axles.
If you're really jonesing for an RB in the car I'd look into going rwd with an RB25. Much much simpler and will still have the sweet sweet sound of the Nissan inline 6. Keeping awd will most likely prove to be a very tricky endeavor.