If there's an ID plate, it'll be on the pillar inside the driver's door. If it's a '47, the ID will start with an "E". '48's start with "F". '49's start with "G". '50's start with "H".
Okay, more clues: If it has a floor shifter, and it's three speed, it's a '47. If it's a three on the tree (steering column), it's a '48 or early '49. However, if it's a '49 or later, the gas filler will be sticking out of the cab, not the bed. '50's have tubular shocks instead of the knee action shocks of the '47-49's. 1950 was also the last year with a driver side cowl vent, so your truck is definitely a '47-'50.
Let us know what you determine, okay?
