Help Identify 8 1/4 differential?

I have been searching for the ID of this rear end for days. The seller claimed it is from a 1974 duster. The actual casting number on the differential housing is #3723599. I have the Motorbooks workshop Chrysler muscle car parts interchange manual for 68 to 74 but is does not list that casting number. Makes me think it may be a different year. In a post by martin7170 to this site in 2007, this is an exact fit for my a-body. Can anyone reccomend a way to verify the year of this unit?
TIA-Rat