If you want to keep it as close to org as you can look for 60,s 3/4 ton that had an auto as it should be geared higher.If can,t find bite the bullet and install a pass diff as it should be no problem unless you are hauling heavy loads...doc
The passenger diff will not swap into the existing housing, and would require changing the whole assembly. That would also require 5 lug wheels, and reduced braking capacity (smaller brakes). If you were to swap the entire rear, one from an '80s/90s model van (Dodge/ford w/Dana 60) will fit nicely. I'm not sure about the GM vans, should be similar exept for the use of the Corp. 14 bolt in either semi or full float, depending on GVW.
