10 hours ago, Zed Head said:

I got curious so I looked in the GI pages of the FSM's. 1972 seems to be the first time they describe the stamping of the identification number on the firewall (cowl).

I wouldn't take that literally if I were you. Their intent was to convey information on location and form in an easily understood and digested nature for people who were used to the national vernacular of their automotive scene, not describe the process with which is was executed.

That's pretty cool! I had thought maybe the firewall was labeled before being included in the chassis but you're saying the chassis was complete and the fixture was mounted to the chassis and the ID number was applied then...