Andrew,

When you have the truck inspected do they look under the hood? If they do, could they tell the difference between what is under the hood and what should be under the hood? If you put the CRD engine in the Xterra other than you (and most likely us) who is going to know? I don't know NC regulations, but I would expect as long as it still has cats and it passes Smog test I can't imagine they'd hassle you.

I know in NJ they don't check under the hood during inspection and they do a pretty thorough inspection of more than just smog.

-Michael