I recently picked up a 1984 Chevy aircraft tug like the one you linked to. They were modified by a company called Eagle Bobtail.
It's got a 6.2L Diesel with a TH400 and a NP208. The T-case has no range selection (I have not yet determined if it's locked in high or low) and it is clocked so the front output is almost straight down instead of being off to the side because the pinions on both axles are centered.
The planetary axles are ZF APL-345/B and, if I believe the tag that is on them, they are 22:1 total ratio (6:1 is in the hubs, the rest comes from the ring and pinion). I plan to confirm the ratios once I get all of the ballast weight off of it.
The axles have built-in 4 wheel hydraulic steering that is controllable via a lever in the cab (regular steer, tight steer, and crab steer options). They also have wet brakes that are inside the planetaries as well as a micro lock for a parking brake. Other ring and pinion ratios and parts are supposedly available from ZF dealers and these axles were also available in some Case International, Ford New Holland, and John Deere FWD tractors so parts can also be sourced that way.
There is no suspension. The axles are attached to the chassis via a centered pivot (like a tractor) and have rubber blocks between the axles and the frame. The tires on it measure 38" in diameter.
The truck weighs 12,000 lbs. and it is rated to tow 60,000 lbs. The front bumper and the box behind the cab are ballast weight, probably about 6,000 lbs worth.
The truck I got fired right up after I replaced the ignition cylinder but its longest trip so far has only been from the trailer to the garage. It will go for a longer voyage once I get all the weight off of it. After that, it's fullsize crawler build time if I can get the axle ratios to something closer to 10:1.
Anyway, here's a pic: (I can get more pics if anyone is interested in seeing anything in particular)
