OK, this is a perfect opportunity for me to increase my "not so useless knowlege" file,...

I was under the impression that the number designation was roughly the tonnage capacity of a truck.
K10-half ton
K15-3/4 ton
K20-one ton
The numbers being tens of hundreds, or 1,000, 1,500, and 2,000 respectively (Thinkin these were later designations for the Chevy's tho).
Then in the bigger bolts, a 3100 would be a 1.5 ton & a 3500 a 1&3/4 ton.

Or,... am I gettin my numbering all screwed up with GMC here? I dunno, gotta ask tho so I can tell these things. smile
Also helps so I can finger out what trucks in the yard I can use to snag parts for my '56 2-ton! grin

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P