Jaksonville for the Z and LA for the MO on mine. MO is built in Kyushu (in the FAQ). Z is built in Opama.
Final assembly....
This is a guess deducing from the Z experience. Since we pre-ordered our Z's we were naturally curious about how many ports they arrived at, how they were unloaded, what was installed at the port yard where the cars were driven to off the boats.
pics here. On the Z, the VIN's were purportedly entered into the system when the cars were in boat transit (some speculation about from the boat or just while they were on board). They enetered several ports and we even tracked the boats for a while (don't remember how many ports and boats but quite a few). Once the cars arrived at port, the record on the nissan web site about your dealers inventory showed up (that's how I knew my dealer had my Z before they did). At the port area, some options were actually installed. For example the optional Aero Kit (front chin spoiler and rear hatch spoiler) was installed. Some deprepping from the boat ride and some prepping for the truck ride to the dealer was also done. It was also suggested that some accessories were installed (rear trunk mat). Oh...and a note about the Aero Kit, we found out because some people had rattles in the hatch which turned out to be sockets left there by the port installers. It was also suggested the NAV DVD and splash guards were installed and checked there as well. A board member purportedly got into a yard and talked to the folks there a little and took a few pics. Others took pics from outside the fence and some claimed to know people in the yards.
So, I'm sure some things are different for the MO, but it gives you an idea of what can be done.