1987 300Es are not that heavy...about 3200 lbs. if I remember correctly. There's really no economical way to lighten the car further, but if you want to try, I'd suggest custom fabricating the hood, deck lid, and front fenders in glass or carbon fibre. After that, you could try a compact spare tire or removing the spare completely. These changes should not negatively affect ride.
I have no idea what the performace gains would be...