if the 300ZX engine is a VG then i'm betting it would swap in fine. I'm also wondering if you couldn't just steal the heads or pistons from it to transplant into the X's motor

I know from experience (not on this particular motor) that simple things like boring the throttle body and even modifying the intake manifold don't ruin streetability. With my truck I lost more bottom end with the headers then I did when I overbored the TB by 2mm and cut the intake runners down by an inch. I'm sure you could do both on the VE with minimal low end loss, but fairly descent high end gain. Couple that with a higher set of gears and the little you lose wouldn't be noticed. I have yet to really look at the throttle body in depth, but I'm willing to bet it has a so called "torque step" in it. Basicly it's narrower in the middle then flares out towards the throttle plate. Simply grinding that hump out would open it up a mm or 2 and allow for better airflow. If you were really ambitious i'm sure a machine shop would do it for $20 or so. All of that also worked fine on the stock computer and passed emmissions. Since then I have reflashed for 93 octane (and gained another 10 to 15 hp), but have no loss in the driveablility or emmissions department.

as for the cams...yea that might ruin streetability, maybe not. It is an "off road' cam, so i'm sure it has to retain a good amount of low end to it. I'm sure NISMO didn't go designing strip cams for the x-terra and frontier. The article I found reviewing the cams also claimed a few MPG gain.