i have a 1996 cavalier lightly moded and recently dynoed at 256 hp n/a and i need help bringing it over 300 hp what whould you suggest.  

Try forced induction. Assuming, of course, that the mods can handle the upswing in horse power due to the increased air. Also take into consideration the fuel requirements with forced induction. And remember that with all that if your electrical power isn't up to snuff as well, i.e.- your spark, you may not get reliable out put. there are a lot of web sites to visit that will cater to American cars, like Summit Racing and Jegs performance. There may be more out there on the net but I would start there just to see what's available for you make and model according to the mods you have made. I hope that this helps you.  

If your pushing those kind of numbers NA im assuming youve got a decently high compression ratio so a lower comp rebuild would be necessary to get those numbers your looking for. You could also look into swapping the supercharged engine from the cobalt. Heard of it being done before but not sure how easy it is.. Even then the engine is meh. Not that great.. Has less power than my car does stock and my car isnt supercharged..