On the subject of power to do the job, this is the kind of truck commonly fitted with slant 6s here and they never seem to have undue problems. They're probably up to three tons:
Slants were very common in trucks here, though the larger trucks had 318s and some Perkins and GM diesels.
When you say 'standard transmission' I assume you mean the truck 4-speed? The one with the granny low? Or do you mean an A230 3-speed?
Frankly, if the poor thing's tasks are only hauling a ton to the local dump, I don't see what you're worried about. Neither fuel nor time should be too much of a concern, in ten miles you wouldn't lose a minute over a bigger engine, surely?
As for the slant 6 and torque, I thought they were noted for their torque? I was just looking at a pile of old 225 blocks and engines yesterday, none of them newer than about 1969 because that was the last we saw of them here.
