Just to clarify I applaud you taking on the project and going in a different direction than using a Calmini kit, whether that was for saving money or other reasons. I understand what you are saying with the Wagoneer axle but unless you compared it's location to that of it's transfer case output and mimmicked this exactly in the Xterra then you might have issues.

If you read some of the replies since I posted I think you get some more ideas on what I was leading to. Fabricating a one off setup is trial and error, but that can be some of the fun of it and when you get your truck dialed in you will be proud at what you accomplished. Now I am trying to remember but doesn't the Calmini kit require you to cut and rotate the knuckles? This is probably your solution as well, a well designed driveshaft is also needed but you might not want to compensate for something you can adjust somewhere else. Keep up the progress and posting of pictures, everyone here learns and gives advice which makes everyones trucks better.