I got the ID# MOO445C071380. Not sure how many they made.Look for the engine code.
FD620D Model Reference (sticker below front accessory shaft, although many are missing)
Engines marked FD620D-AS01, BS01 have a plastic cam gear
Engines marked FD620D-CS01, DS01 have a steel cam gear
Tractor serial number for the steel cam gear starts at 60001, which is 1998.