Hello, Mike. Welcome to the forum.
Your truck ID number does not comply with US truck VIN numbers.
http://www.stovebolt.com/techtips/VIN.htm
If it is a VIN number, it looks like the series is missing. The remaining information would decode to 1956 model year, produced in unknown plant (2) with sequence number 003138. This is speculation though without more information.
If the truck was made in North America then you might be able to contact GM USA or GM Canada to obtain more information.
Do you have any pictures of the truck? Does it look like other US trucks or are there unique differences like Canadian trucks have?