The numbers for the gear box are on the right side towards the front on a machined pad about 1x3 inchs long. The information contains Car VIN information and also the gear box build information.
Understand, it will likely not be a full vin, but year stamp, factory of car origin stamp, and the last 6 of vin.
As in the example 68FS340 posted is from his 68 gear box. a simple decode of his is 8=1968 B=Hamtramck and the last 6 of his vin. I was used instead of of 1 on body and engine. Each Factories VIN started at 100001. which makes his the 53,909 car off the Hamtramck line of all models built there that year.