I scored a VQ35DER from my buddies wrecked 2006 350Z with only 18K miles. Very unfourtunate for him. I felt bad for him so I bought his engine and trans to help him out...
On the way back to my place I weighed the engine (complete w/o AC compressor) 6-speed transmission, wiring harness and electronics and it came in at 580 LBS total.
After stripping the engine and trans down I noticed there are tons of places to loose weight like misc. metal brackets, power steering pump, metal dampers, and a 45 LB clutch and flywheel.... yes 45 LBS! apparently the Tilton clutch and flywheel set is the way to go with these engines.. 14 LBS..
I first plan on getting the engine dropped in with a crossmember style engine mount and then tackling the wiring to run the stock ecu.
I definately have to run a fuel return so i'm going to mod the fuel rails just as Austin has. As far as exhaust goes I still don't know yet but, I sure don't want it to sound very civil like your ordinary G35 or 350Z.
I'm excited as i'm hoping to loose around 100 LBS and gain 100 HP from my previous setup. Also the tightness in gear ratios of the 6-speed is going to be a big plus.