The moderator are pretty dang good at coming up with those member captions.
Ali, do you happen to have the 350z differential on hand? Take a quick look at it, then crawl under the 240z and take an even quicker look at that one. Also, brake upgrades and drivetrain upgrades are two completely different things. You certainly can upgrade the brakes and use your stock diff. Just not with with 350z ones. Well saying you can't is perhaps a strong way of putting it, but like say, alchemy, it wouldn't be the greatest idea ever to try.
Either way, for all intents and purposes your question has been answered.