Late 70's - early 80's GM will fit the bill. If I remember right, a big block is a direct bolt up to the diesel trans.
The other option that appeals to me would be a first generation 90-93 Dodge/Cummins.
I don't know about PTO availability on an auto trans, but it can definitely be done with a granny low 4 speed. If ya go auto, a MileMarker hydraulic winch might be a better option.
Ford did have a "swiss cheese" lightened frame for a few years, had an '80 F250 like that.
On the military trucks, rust should be minimal, but if you're gonna paint it, it's gonna need a TON of prep work. That military paint is thick with one coat, and there may be lots of layers on there. Dodge M880 I think had 360 gas, and the Chev CUCV was a pretty anemic 6.2, but we ran em alongside our M915 semi trucks, and they'd go down the freeway at 70+, just took a long ways to get up to speed.
One other thing to note in the srw vs drw debate is that duallys really suck in mud and deep snow, the space between the wheels fills up and you've got a huge slick back there. I'd go SRW myself if only for that reason. Duallies are highway trucks, period.
all of my trucks are duallys and work fine in snow or mud, just have to have good tires on them, log trucks are duallys and also work fine off road, DUH