Two floor jacks and/or two extra jack stands helps position the axle. When you remove bolts from shackle, the extra floor jack will help make slight adjustments to spring position to relieve pressure on bolts and bushings. Same for spring eye. I did both springs at same time, though one at a time is easier.
An air hammer is really nice to drive out old bushings from shackle hanger.
Wait to torque u-bolts until you get shackles re-attached. You will need the play on the spring to line things back up. Don't over torque the shackle bolts. Also don't torque spring eye bolt until weight is on spring.