When penetrating oil and a drift (edited for auto incorrect) punch does not work on leaf springs fasteners, I have resorted to a recip. saw. If you can fit a blade in the bushing without cutting the car, that might be a final option.
I swapped a T-Bird Super coupe rear on my car awhile back. I did it by myself with beer power, took a weekend. Uppers first, then keep the axle on the Jack. Manipulate the Jack height to get the lowers in place.