Welcome to NICO, Motorsport Nut!
Here are some detailed sales numbers for various Infiniti models, including the USDM Y34 (2003 and 2004 M45) and the USDM Y50 (2006+ M35 and M45):
zerothread?id=191187. I need to update these charts, but you get the basic idea!
In Japan, the Y34 chassis was available in both Nissan Gloria and Nissan Cedric models, although, AFAIK, without the 4.5 liter V-8 that we got here! In the US 2003 and 2004 M45, it was only available with the 4.5 V-8.
The current Y50 chassis in the 2006+ M35 and M45 is in the Nissan Fuga in Japan. Although, I do not know if the Fuga in Japan has the 4.5 liter V-8 ... does anyone else know that info?
As GJEMD noted, the 2003 and 2004 models are essentially identical, with only minor cosmetic changes and options.
For more details on the car specs, colors, etc., please see the Sticky thread on Basic Specs at the top of this forum.
Thanks!
Z