You can find a lot with
http://www.google.com about weights and whatnot...
As far as going 8's...
go for a well built RB (25 or 26 most likely), have nothing in the car (and hold off on the fast food and soft drinks), replace the windows with lexan, well built trans (hear the 20... not sure on the other two trans go at 400hp... look around and i'm sure you'll find out), and a well thought out gearing.
I am sure by the time you get here you are well past 4k... so I'd say this...
Get a cheap 240, strip the car... drop a pushrod V8 in er w/ a used blower, throw a 200 shot on it, and back it up with a 8.8 rear end with a posi diff... you'll hit 10's maybe... and just barely get under your 4k limit... maybe.
Granted... at this point you have defaced the Nissan name... but like many other cars I don't like... it's not mine.
Good luck bud