Flat bit toward the front, the rusty looking bit!
I had the same problem with jacking when I first got the Z too, the drawing didn't really show much and like you said it didn't seem right to jack on the diff.
You won't have the knob on the HR, that's why you can't see it
Best pic I've got, of mine. There's basically a flat area behind the fins on the diff, that is where you want to jack it.
Edit-
Found another pic of mine, should be clearer:
The HR air boxes with panel filters are proven to give you the best gains if you are looking for power increase (after a remap though, you won't get any gains at all from just adding breathing mods). With cone filters etc you tend to lose a bit of power (not really noticeable) but you do gain engine noise.
Very pleased for him, considering the **** up yesterday. Would've been interesting to see if he'd got past Nico if he hadn't had a gearbox failure, the gap was getting smaller and smaller..
Just drive to the conditions and you will be fine, you'll poo yourself the first time the rear end goes in the rain but you will get used to how the car reacts with experience.
It's easy, just got remove a few bits first. There are several guides on the internet you can follow. Also you need a thin walled socket to remove/install them.
Amazing that such a heavy car can get round the ring that quick, powered by just a twin charged V6. There's no denying that it's an incredible car.
http://nurburgringlaptimes.com/lap-times/lap-times-top-100/
To be honest though, if I had £125k to spend on a car, the GTR Nismo wouldn't be top of the list.