There's heaps of estimation in this thread which really doesn't help anyone at all. I seriously doubt eliminating HICAS is 20kg's worth.
What is good though, is that you have a target weight figure. That helps a hell of a lot. Get it weighed, then start from there... it'll make it a lot easier.
The R32 GT-R in dead stock form from the factory showroom is 1480kg's. That's a heavy mofo. The Group-A racing cars were 1200-1300kg's. The N1 version (only a few made) were the same as stock but without ABS, boot lining, stereo, rear wiper/motor + aircon to save weight (surely not that much weight savings there).
I haven't bothered with saving weight as it's been so easy to add power but I have taken out some carpet/tar, rear wiper/motor, rear seats, belts, lighter seats but mostly I've added a whole lot of chassis stuff... full cage, bracing up top and under the car too.
After a weighbridge at Mascot (you pay $22 to get your car weighed) I got a figure of 1480kgs!
So spot on I've managed to keep the same weight as stock but have a gazillion mods on the car. I'm baffled as to how they get their cars down to 1200kg's though. I know I can save a fair bit if I took out:
Aircon (anyone weighed this yet?).
ABS (works pretty crappy I find on an R32 in any case).
completely remove hicas (rear wheel steering rack).
lightweight battery
stereo
But that's a fair bit of commitment right there. Something I am thinking about in any case. Shame that when I put 6-pot AP's on the car my weight will go up again... 355mm pizza sized rotors have got to be heavy!!!