I would concentrate on unsprung wieght like the diff. I stripped my car then concentrated on get the cg lower...dropping the motor tranny and mounting things as low as possible.
Whenever trying to get a car light I always remember a story of a California GT3 team. One car was built right to the wieght limit the other was for actress Marsha Mason....she wanted the car to be safe as possible so some more tube was added. Well the go fast car breaks and Mason graciously offers up her car , so the team can get points. Well Her car turned out to be faster due to the stiffer chassis....I just keep this in mind when trying to lose another 100lbs .
Keep in mind I weigh 135lbs so my car can afford to be fat.

Tom