The differences between a 1/2-ton and 1-ton panel are obvious: 8-lug axles/wheels and a significantly longer body (personally, I think it's more proportional). My '54 GMC 1-ton is about 19.5 feet, bumper to bumper.
BTW, that serial number looks a bit short. If you post pics of the serial # plate (and the whole truck), we can do a better job of identification.
