I think the sheriff has a few things mixed up. GM trucks did have id plates from the factory, but prior to the 50's they were screwed on vs riveted. A number of muncipalities across the country would us engine numbers as the VIN instead of the id plate, which creats a whole new set of challenges if the motor it was titled on is no longer in the vehicle.
Reference from Jim Carter's
http://www.oldchevytrucks.com/blog/i...tag/id-plates/