Here's some more info on 6100 trucks.
http://chevy.oldcarmanualproject.com...esto/54109.htm
Looks like the 6100's were "2 ton trucks" and the the 6100S is a slightly lighter version with a 1 1/2 ton rating.
It also looks like they came with 261's not 235's. Which is better for your needs. Of course neither one is going to get you anywhere fast.
After 64 years of service, it's hard to tell what had actually been done to the truck over the years and what it is actually equipped with. You'll just have to dig in to it.