The last thing I want to do is to talk you out of a deuce. All the more so since I have one to sell you....
But let me muddy the waters a bit though -
An 809series 5ton is like a larger deuce with power steering. It'll be no more complex to work on, although everything is heavier. The engine is an 855ci Cummins NH250, with a life expectancy in heavy truck use of a million miles.
The 939series is essentially an updated 809series truck. These have automatic transmissions and full airbrakes. The cabs are also a bit larger. The A0 and A1 have the same nh250 as the 809series trucks, while the A2 has an 8.3 liter turbo diesel and CTIS. CTIS can be easily disabled.
There's no bad choice. You can essentially pick any one of these (including an M35A2) at random and have a very good choice for a toy and a project
You mentioned your father likes an automatic transmission and power steering. That makes the 939series a particularly good choice.
My own choice is a 939series 5ton, A0 or A1. And I'm one of those guys who prefers a manual transmission. The full airbrakes are what make it for me. The A2 variant is clearly a better over the road truck, but for use as a toy there's really no reason to pay the premium that the A2s bring.
I realize that I covered this on the phone. I'm throwing it out here in written form to allow other people to add their perspective to it.
