Chevy produced the following partial trucks
Cab and chassis which would have been a full cab (3603)
Flat Face Cowl chassis which is a cowl with no windshield or doors. (3602)
Windshield Cowl chassis which is a cowl and windshield also without doors. (3612)

Take a look at the vehicle info kits. Example

Everything else would have been farmed out to a body builder. The same thing happens today with Class C motorhomes. Chevy sells the partial van and chassis, usually with doors nowadays, to Winnebago, or whoever, and they build the rest of the rig.

That looks to me like a cab that had the back cut off. If it was factory, why would they have used a 5-window cab quarter panel?

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.