On the R32 25DE the cams are different (32 style to not suit VCT), the cas is different (again R32 vs R33), and you need to upgrade to GTR valve springs as the R32 25DE springs will start to give valve float with not a lot of boost.
http://ripsltd.com/products.html
that basicaly goes through everything. if you are only looking for 300-350kw range the stock internal bottom end is fine (good for 600hp and 7200rpm) remember that all pricing on their site is in NZD not AUD.
You can make 350kw on stock cams but you need more boost than you would with mild upgrade cams say tomei poncams. sure you can make the power but there are benefits to the upgrade when you are at that level of power.
from memory it depends which power steering pump you are using, and if the belts line up correctly. Assuming the alternator/water pump belts are the same.
but for the price of the ross units why not just get one of them?
Item: Apexi Power FC Boost Control kit
Age: 18 months.
Condition: Good.
Price: $350 inc shipping (Firm)
To Fit: RB25DET With R33 Power FC
Location: Canberra.
Contact: Steven 0419 302 418
It does come with the cable from pressure sensor to the ECU but not pictured.
R32 GTST is 1320kg
R33 GTST is 1370kg
R34 GTT is 1410kg
i don't know where you are going to find the factory info but that's the weights to the best of my knowledge.
All of which are lighter than an R32 GTR.
i haven't changed the sensor and don't remember off the top of my head which wire the relay is attached to, the AC thermo fan has been removed from my car.
Mine currently runs twin 12" thermo fans. Sits dead on 80 for all street driving and spirited driving. only starts to go to ~90c when you really push it hard ie a track day in summer (standard radiator and thermostat)