I think VIN tags did'nt realy start untill 53 but I kinnda remember working on a 49 and seeing a tag in the door jam . I allso remember working on a 50's model and only seeing a vin on the frame like "Mopardude" said . Sorry could'nt be much help .
you can find the ID plate on the door pillar, left side between the hinges. But if it missing, you find the Serial number hand stamped on the left frame, near the left front spring hangar. should be 8 digits, no letters.
Dave www.39-47dodgetrucks.com