I have a '71 Malibu with a factory 10 bolt non-posi unit that just saw its last day. I now want to upgrade to a 12-bolt posi differential. Which units will interchange with a '71 Chevelle? Is it any '68 to '72 A-Body? Is there anyway to tell by coding on the differential itself? I know some yolks have "lips" that ensure the U-Joint is centered properly (like mine now)and others dont. Anyway, if possible, I would like to find a 12-Bolt that was originally out of a '71 Chevelle. Any help would be greatly appreciated...Thanks in advance, Tom