You can decode the body serial number. Tells where it was made and which one and the year made. Your tag may have been just screwed on being a 49. Maybe taken off for a fresh paint job st some point? Maybe you'll get lucky any find it in the truck somewhere.
Not sure if panels decode the same but this is the site I used.
http://www.sanjosechevys.org/Tech/te...chevtrucks.htm