The 68 has partial vin stamped top center where auto trans and engine mates. Not sure about bell housing, manual trans case has partial vin stamped on pad.
There is a lot to do verifying so and vin. Date codes of various parts relating to scheduled assy date of car. Even the batches of so #'s can shed light (with some variances) when compared to the vin sequence.
A12, I think that is generally the engine plant, shift, and maybe date, need to check to be sure.