I have replaced bushings without dropping the whole spring, but it is a ROYAL PAIN!!! You can open the eye a little with a screwdriver or chisel. That will help. The biggest problem is getting something heavy enough behind the spring to support it while you pound out the old bushing and drive in the new one. You will DEFINITELY need a strong friend to help you!
If you pull the springs, you can lay them over an anvil. I use an old 6 cylinder Chevy block I have in my shop... good use for it since it was cracked anyway. It is still easiest if you have a friend hold the spring while you pound on the bushing.
If your U-bolts are rusty and will probably break, you will suffer one way or the other... choose which way you prefer. If things aren't too rusty, it would be easier to drop the spring. We replaced the front springs on the old '92 a couple of weeks ago. It has seen road salt only a couple of times in it's life. Everything came apart like it had just rolled off the showroom floor!
Something else to consider is the position of the shackle on the passenger side. From the factory it is installed in such a way that you have to drop the exhaust to get it off or take it apart with a torch and replace it. If the upper bushing is still good, you can drop the whole spring and get it out. If you leave the springs bolted to the axle, you will have to completely drop the whole spring and axle assembly and drag it to one side to get it apart unless you drop the exhaust or cut and replace the shackle. If you remove the shackle, you can install it with the nuts inboard so it will come apart easily the next time.
Steve