REAR Clunking Sound when turning

Check the mounts for the leaf spring shackles. I had a 74 Dart that the mounts rusted off the frame rail and the ends of the leaf springs jammed up into the trunk. I bought it a little time by bolting a 4 x 4 thru the frame rails and using lag screws to hold the shackle mounts to the 4 x 4's. Eventually scrapped it.