Need the rear frame to body rubber mounts and bolts. They are two piece mounts. One goes on the under side of the frame and the other one goes on the top side of the frame, and when bolts are installed, the frame is sandwiched between. There are a total of four pieces to the mounts. Two on the top and two on the bottom. Then the bolts hold them in place.
So GM no longer has them available? Rockauto doesn’t have an aftermarket set?
Welcome to the world of old cars. I would suggest you look at replacement body mounts being reproduced and sold by several different sights. Late Model Restoration for one. You should be able to find something close. The bolts can be bought from Grainger, McMaster Carr or Fastenal