Welcome to Stovebolt
The number on your firewall JBA308473 is an engine serial number. The engine serial number will be stamped on the passenger side of the block next to the distributor. Pre 1955 the engine number was the number used on the title by most States. This number was never stamped on the Cab by the factory (your numbers look hand stamped, not machine stamped). If you engine was replaced at some point the mechanic could have transferred the number there to connect the title to the truck.
Your number breaks down as follows...
JBA = 1951 216 engine from a 3100 truck built at the Flint engine plant.
308473 = unit number out of Flint starting with 1001 for the model year.
Does this number matches your engine and/or title?
What's the number on the door post?
Mike B
