They are heavy, but I think the most savings is from getting rid of the beam in the bumper that the shocks bolt to. I was lucky enough to be able to swap mine for aluminum ones from a Feather Duster.
It seems like my car is one of the few 1974 Dusters with shock mount bumpers both front and rear. In the case of the front frame rails, mine still has the holes for the standard bumper but no threads. The rear is really different and missing sheet metal to make it work.
What would be really cool is if you could figure out brackets that bolt to the bumper without the beam and used bolt holes that are existing in the frame rails. Oh, and pulled the bumper in an inch or more. I bet people could drop 100# or more off the car if they could replace the shocks and beams with an aluminum bracket.
