Replacing the bumpers with fiberglass replicas is worth at least 100 pds. Getting all the tar sound deadener out of the car is worth another 150 pds usually. Factory seats weigh another 100pds, you may be surprised to find the carpet weighs another 50pds too.
One of the heaviest thing on a car is the glass, kind of need the front windshield as a minimum though. To give you an idea how much you can lighten a car, I brought my 81 Mazda RX7 from 2400pds factory to 1900 pds just by doing the items listed above...and that was a small car!