Woogeroo,
I don't know if this holds true to GMC's, but on Chevrolet's, the dust cover on the front spindle screwed on for 1 1/2 ton and was held on with little bolts for the 2 ton.
Although it isn't real clear in the pix, it looks like these are held on with bolts. Maybe a TWO TON!
It looks like a 12' bed to me!
Stuart