Replacing rear shackle bushings on your later model Studebaker is not a bad job if you make a tool to remove and install them.
You will have to start by getting a piece of 7/16" USS.all-thread rod from a nut and bolt dealer. You will need at least grade five rod, not the kind they sell at hardware stores. The rod will come in three foot lengths and you should get at least eight nuts to fit, 11/16" wrench size. You can get the threaded rod at McMaster Carr part number 98957A610
While you are there get a metal spacer that has a 7/16" center hole and a outside diameter of 7/8" or.875 and a thickness of about 3/8". You will need a piece of pipe 3" long with a inside diameter of one inch and the outside diameter will be about 1 3/8" but the outside diameter is not critical.
You will also need some large diameter, over 1 3/8", flat washers with a 7/16" hole. Get a few of these, six or so as you will bend a some. I find that cutting a piece of threaded rod about eight inches is a good size for most cars. If you are working on an Avanti you will need two different lenghts because of the small clearance from the spring to the body work.
Jack up the car and put jack stands under the frame. Position your jack under the differential, and apply a little pressure (raise it 2-3"). You can then remove the through bolts at the spring and shackle.
I start by replacing the bushing in the spring first as it it easier and you can get familiar with the procedure. In theory you put the threaded rod through the bushing. put the 7/8" steel spacer on and a nut. Then on the other side you slide the pipe spacer on and center it over the surround shoulder on the spring, put on a couple of large washers ( a little lube here will prevent galling) put on a nut and tighten to withdraw the bushing.
In practice the bushing is worn and off center and it is impossible to center the 7/8" spacer. I just forget the spacer the first time and put a nut on it only. Then tighten the nut at the pipe spacer until you have withdrawn the entire rubber center from the bushing.
You can repeat the procedure with the 7/8" spacer centered on the old bushing and withdraw it. This may require a couple of 11/16" box end wrenches about a foot long!! If you bend the threaded rod extracting the old bushings, it it time to cut a new piece and continue.
To install the new bushing you can either cut a section about 3/8" from the old outer bushing case or counter drill the spacer so that when you use it to pull the new bushing into place you apply pressure only to the outside steel part of the bushing.
You do not want to apply pressure to the center steel part of the new bushing. I use anti-seize on the outside of the bushing. I do not know if it makes them easier to pull in but it will help the next fellow in 2032.
Once you have successfully installed one bushing in the spring you will have the experience to do the others and the ones in the frame as well. At this point raising or lowering the axle to align and replace the bolts in the shackle is a rather easy task. I re-check the torque on the bolts once the car is back on the ground at ride height.