Well actually '55 to '59 or some part of that period, it was possible to buy a 3/4-ton with duals from GMC. I don't know if Chevy had a similar model or not.
The second pair of numbers in a Chevy model number usually indicate body type and maybe wheelbase. I'm much more knowledgable about GMC numbers than Chevy, and in both cases its the '47 to '54 trucks that I've spent most my time with.
Perhaps someone else will come along and explain those model numbers?
