Well if you go lean you will burn a hole right through the top of your piston. Barring that, a whole slew of things can go. The thing you have to keep in mind is the cylinder pressure goes up as the amount of boost/nitrous increases. If you're lucky, you will blow a head gasket. You could probably blast the top rings, shatter a piston, throw a rod, or blow a hole in a cylinder. I doubt you could stuff enough air into the 3.3 to blow the crankshaft out the oil pan. So essentially the weak points would be just about everything below the heads. Of course, there isn't a guarantee of anything above the block either.

The key here is moderation. Remember Grasshopper... the louder the bang, the more expensive the fix.