Manual Transmission VIN Decoding

Anyone know how to decode transmission VIN numbers? I want to verify another source on this as im coming back as 28L = 2= Feb 8= 1968 L=Plant

Also the main case casting number is 3925658 which comes back as 68-75?
Tailshaft cast number is 326558 which comes back as 3 or 4 speed

picture is posted of the VIN stamp

I only ask because im getting someone trying to tell me they didn't even make saginaw's in the 60's even though theres literally dozens of sources including GM books showing this casting number first in use starting in 1968

Biggest thing im looking for is the correct read on the VIN number if anyone has info on that i'd like to nail this down to a specific year and model if possible

Thanks,
-OSK