I have tried hacksaw method, socket on end of air hammer, mini-sledge, etc. The only way to go in my opinion (other than elusive KR Wilson tooling) is the "hot wrench". Simple, easy, quick, and effective. Make sure to clean and debur hole before installing new bushings-it will make your life a lot easier...
Let me clarify: heat center stud with torch, this will burn out the old packing material and allow the stud to literally fall out. Free by product is that you also may have broken the rust bond of the shell to the axle housing. Try a socket and hammer to see if the shell will move (it probably won't). Don't be too rough or you will wrinkle the shell and make extraction even more difficult. Use hacksaw or similar tool to cut a slit in the shell to relieve tension and then drive it out with socket. Clean and debur housing before installing new shackle. Do not worry about aligning the square shoulder on the stud for the shackle links. These are easily turned with the link when reinstalling the spring.