Behind the driver seat from what I remember, remove the folder holder and the unit hides in there. That's on 370z 2009, not sure if you have Connect Premium it's different.
Josh, buy an UpRev cable, useful to send logs to Jez in case you have problems, he can tweak your maps and send them over to you so you can upload them, you can check and erase faults etc.
£849 from what I remember.
It's heavy and needs to be packed properly to arrive here safely, so big box which puts the cost up. Factor Duty, VAT, handling fees, shipping...
Do you need bearings as well?
Find a place to repair yours for a few hundreds pounds.
http://www.aaagearboxes.co.uk/gearbox.html
http://www.bktransmissionsltd.co.uk/bktransmissions-pages/home
http://www.bristoltransmissions.co.uk/parts_manual_gearbox/
http://www.expressgearbox.co.uk/contact/
http://www.a1premiertransmissions.co.uk
http://www.staautogearbox.co.uk
and so on.
I think the forum needs a proper specialist that can fix the 350z gearboxes cheap and quickly, I've seen so many people in here complaining about the gearboxes failing.
Sounds like an airlock to me, worth trying to bleed it again.
Also, Mishimoto Radiator and Mishimoto Fan Shroud should help a lot with the cooling, both in stock if required.