Eric,
GM did not use the term 1947 first-series. There was a 1946 series and a 1947 Advance-Design series.
Unfortunately, a 1946-series truck built in early 1947 might have a 1947-dated engine. If you are in a state that uses/requires using the engine code for titling/registration purposes, you will have to go with the year of the engine. In New York, we call register using the Vehicle code or the engine code (I have had VA and WA registrations using either code).
Do you have an old title or registration for the truck?
