Thank you again to all who helped out. With a bit of luck today we returned to the wrecker in question and actually found a tailshaft that does match!

The length and width of the shaft was that of the 120Y manual shaft but the flang on the diff side was precisely that of the auto. Upon cleaning the shaft we found the words "Dat Sunny" written on there indicating that it was indeed directly from a Sunny.

Saved ourselves $150.