You get way more tourque out of a 4bt and the trans, transfer case and diffs will not hold up to this torque monster. If your going to do this, you really need to change the whole drive line and the sas will be a must, due to the engine hight.
You will most likjely need heavy duty diffs and have them cut down and shorter axles made.
This ain't going to be easy, but you will have one bad ass Xterra when done.
I hope you are up for the task and have the funds to pull it off!
I have a Dodge Dually with a Cummins (6bt 5.9 L), chipped, large exhaust and intake systems, 32 psi turbo, larger injectors and it is making 1000 lbs of torque. The rear diff is a dana 80 and the front a 60 (it is 4X4) I can not imagine the Xterra running gear holding up at all, even to a stock 4bt. You need to think seriously about changing the whole running gear!
Best of luck and keep us posted
2000 X SE
V6 SE 4X4 5spd Build and 00 Silver auto SE 4X4http://www.clubxterra.org/forums/showthread.php?t=26084
Raise TBs (X), paint plastics (X), Replace radiator with one that is bigger and will last (X), install roof lights (X), IAB (X), better tires (X), shackles in rear(X), remove rear sway bar (X), Bilsteins (X)