Update.
I called some of my old junkyard sources around where I went to college. I used to (while I probably should have been studying more....
) beat the bushes hard for stuff. I think I found a 12 bolt from a '71 Chevelle SS. It is a non-posi. The guy said he would have to put his hands on it.... but if he didn't rob an axle off of it..... he would take $250 for it. Does this sound reasonable. I told my friend..... at minimum.... I would put a posi in it.... some new axle seals... and a new pinion seal..... and repack all the bearings. I am sure the brakes will need refurbishing as well.... if they are still on there. Will his 8.2" 10 bolt brake drums and hardware work on the 12 bolt? Are the bolt patterns the same? What do you guys think the gear ratio was for a '71 Chevelle SS? I am going to guess somewhere between 3.42 - 3.73.