Rear differential info on fender tag ?

Did,a little more research, saw a fender tag of a real 440 Dart. Apparently the Hamtramck tag does not show the drivetrain build codes , like my lynch road b-body tag does. It doesn't even show any "A" codes. Just the "M" and Y39.
The tag I saw is for a car that the owner had professionally restored, and claims it has the optional 3.91 gears.