Newbie Question 31 vs. 32

[FFredo]

I'm new to Chevy Trucks and as I work on bringing my 59 Apache back from disrepair I continue to learn what is what. One thing I have not been able to find out is what is the difference between a 31 and 32 designation?
According to my serial numbers I have a 1/2 ton assembled in Los Angeles.
However I have 32 fender emblems, also there is a set of "stops" mounted above the leaf springs on the rear. They are attached to the frame and look like they are designed to stop travel before the rear end hits the bottom of the frame. I'm only guessing here but I think that means my truck is a heavier duty truck...but still a 1/2 ton? Is there such a thing as a "heavy Duty" 1959 1/2 ton?

Thanks in advance ya'll.

Fredo