This may not be worthwhile even if it is possible but I still wonder when doing a 3.5 swap.

Would it be possible to use the 3.5 Maxima or 350Z ECU to only operate the VTC and then continue to use the 4th gen ECU to operate everything else, or would the 3.0 timing components or other components stop that from even being possible?

 

You have to pick one or the other.

If you are using the 3.0 timing arrangment, you would not have VTCs to begin with.

 

I SERIOUSLY doubt this is possible, but what about if you have EU?

 

EU can't control that, and like eng92 stated that if you use the 3.0 timing you are unable to have VTC. You would have to use the 3.5 timing to do that which would thus mean you'd have to use the 3.5 harness.