Is the rear end sitting on the bump stop on one side but not the other? While highly unlikely, you may want to look at the rear shocks. I would try swapping springs left to right, to remove them from the troubleshooting scenario. Then do the same for the shocks. While you have the springs outs, look carefully at the mounting seats. Springs are supposed to dictate ride height, unless something is binding. From your pics, I think you have a ride height problem, not an axle centering problem.