1) any difference in chassis from sourer vs. sc300
There is next to nothing in difference apart frmo just a few luxury's that don't appear in the SC300 but do in the Soarer, one thing I did find was the dash display, SC300-Analog Soarer-Digital and there is no way of converting from either !!! There are a few other little bits and pieces but for what you want to do I guess it would come down to personal choice.
SC300 - less luxury and options. ;)
Soarer - Seems to have almost all of them.
SC400 - Always loaded. :P
2) how much weight difference is there from sourer to sc300
The main difference in weight is the engine, the SC300 comes in the 3ltr 2jz motor, the Soarer comes in the 2.5ltr 1jz motor. From memory the curb weight for a Soarer is somewhere just shy of 1600kg (phat boy). But when you start removing alot of the luxurys you'll get a lighter car, a good point of reduction is the doors !! they weigh 50kg+ each side so some carbon fibre replacements will do the trick in lightening and I believe evening it out for drift application. B)
3) how much does the sc300 weigh without driver
See above. :)
4) is there a better year to get for the sc300 ive noticed 92-99 just wondering if some years are worse or better then others.
Try for a July+ 93 model. Majority of the ECU problems have been ironed out (see the model differences chart somewhere). If you are looking at replacing ECU all together then I guess you choice is to VVTi(95+) or not VVti(95-). <_<
Hope this answers your questions and please keep me in the loop about your project as I've read a little about doing the change over myself.
Someone needs to put those Nissan kiddie drifters in their place. :D