years ago i was given a chrome bumper for my 53 GMC 3/4 ton pu. it slid right onto the outside of the frame rails like it was custom made for it. it came off off a 70 GMC 3/4 ton pu. (kindred spirits?)
based on this maybe a rear end from this vintage would be workable.
I just replaced the rearend in my wife's '94 'Burb. it is a 1/2 ton. the spring perches for the 'Burbs are fidderent from the trucks of that era. that being said, in '94 only they made a 6 lug 1/2 ton 14 bolt rear end for the 'Burbs as part of the tow packaage.
If you live in the Portland OR area there is an all GM yard called 205 Auto Salvage that has really nice parts. all late model but, if you are looking to upgrade your power train...
