Do you have any ID codes? You indicate you have the ID on the title. If so, please post them.
Here are a lot of technical specifications on 1951 Chevrolet trucks. A wide variety of "adaptations"/swaps are possible between 1/2 and 3/4 ton Chevrolet and GMC truck parts. The frames and wheel bases are different between 1/2 ton and 3/4 ton Chevrolet trucks.
Helper springs were readily available from after-market sources.
If the driveshaft is totally enclosed, it would be a 1/2 ton truck. As you noted, there were no long-bed 1/2 ton 1951 Chevrolet trucks.
