For the purpose of comparison, here is the 350Z engine compartment as it currently exists. The 2007 350Z - to be announced in January - will feature the improved 3.5 V-6 from the G35 (unfortunately a move to the improved "FM" platform is a few years off).
Comparing the picture here with the 2007 G35 engine picture below, we see that some re-shuffling will be needed undere the hood. One question that is unanswerable at this point is whether the 350Z will need it's hood raised to clear the new engine. A limiting factor of the current Z engine is the very low intake manifold... does the new engine have a taller intake?
Unfortunately, we won't know more until January when the 2007 Z announcement is made.
Continue to Yahoo autos for information on the 2006 Z.