I didn't go all the way with removing the spring, but to take the load off the spring what I did was:
- Loosen the lug nuts
- Prepare some jack stands at their max extension
- Put a floor jack under the differential
- Raise the differential until the frame is at the level of the jack stands
- Get the jack stands under the frame
- Remove the wheels
- Lower the floor jack
At this point there is no weight on the spring; you should be able to attach the spreader, remove the U-bolts and shackles, and pull it out.