I had the same thing on my 71 and I like so many put a coil-over shock on the rear. They made it look great but in a year or two Inoticed a noise that was hard to identify. The extra pressure had broken the top mounting bolt that is set into the frame. It was an easy fix but went back to standard shocks and installed new springs to get the original ride hieght back. Good luck with your rebuild. Old Irons Rules!

Adding overload springs around the shocks or putting on airshocks, will eventually do more harm than good. You are putting too much strain on the body of the car. Using leaf spring shackles has been the accepted norm because it keeps the load where it should be...on the suspension and frame.