This is not a build tag per se, it's a "buck tag" used by assembly line workers to make sure the installed parts match the vehicle order.

Truck was ordered by a US Gov't agency with a heater (optional), left front door lock cylinder (optional on Standard Cabs), rear channel bumper (all rear bumpers were optional thru at least 1979).

The "buck tag" on the seat is related to the seat maker only. Again, it was used by assembly line workers to make sure the seat matched the vehicle order.

All seats have "buck tags" because all were bought from outside suppliers. If y'all think that FoMoCo makes all the parts on their vehicles, think again. No more than 10% of the parts are made by FoMoCo.

That's why they're called assembly plants, because vehicles are assembled using a gazillion parts shipped in by 100's of different suppliers.

All these Crew Cabs were outside conversions. FoMoCo didn't offer a factory Crew Cab until mid-year 1965, and it too was a conversion from a Regular Cab, as were 1966/72 Crew Cabs.

Look in any Ford truck parts catalog prior to 1973, see if you can find ONE specific Crew Cab part. Lotsa luck, cuz there's nary a one.