I think Stu was referring to stamped date code numbers and potential manufacturer designation ?
Anyway, this is a tough nut to crack..
Talking about difficult, try running down info on a 70 Manual Drum Brake Master Cylinder ( Dearborn ).. According to the 70 shop manual, there's an I.D. mark stamped on the end of the MC.. Mine is stamped but nothing to compare to for I.D.