I'm not too sure what it came out of, but the leaf spring bolt holes are 44" apart and the backing plates are 51.25 inches apart (Measurements are close, but may be off slightly).
Sounds like you have a 66-70 B Body rear end. Could be interested in the pumpkin if you care to split it up. What kind of parts you;d be interested in?
EDIT: You need to post a price or one of the mods might delete your ad per the rules