Some of them get rust/rot from sitting, especially the ones along the east coast.
Rear suspension rubber bushings can be prone to dry rotting and needing replacement.
I would not worry about the ABS either way. It generally is there on all of the 923's, 923A1, and 923A2 trucks. The US military decided to upgrade all the trucks with ABS due to them having excessive brake force in non ABS form. I can imagine that some of the very old trucks might have got missed in the upgrades. It really does not matter or affect the driveability anyway if you plan on driving it with reasonable respect.
Shop around. I have seen some of the Kijiji advertisements in Ontario and they seem to be fairly spendy, sometimes as double what they are really worth. I often see them advertised before they are even imported, and the pictures they attach to the advertisements are the thumbnails from the military auctions. It is pretty tough to get a good idea on the condition of the truck from those images.
The CTIS is pretty cool on the A2 trucks. If you are into some serious off roading it comes in handy to increase the contact patch of the tire in low traction conditions. I have not had any problems with the CTIS on my trucks, but some people (including military mechanics) say they can be trouble prone.
The parts for these trucks are pretty much only available in the USA. So if you do need to take care of some mechanical work expect to buy the parts down south and wait for the shipment. In your business I am sure you can understand the frusteration of sourcing items and dealing with shipping.
The M923 with the Goodyear radials (dual rears 11.00R20) will top out about 55mph. Any of the trucks with the super singles will move along quicker due to the larger tire diameter. All of these trucks have the same differential ratios in them. The NHC250 (855cid) and the newer 8.3 turbo cummins engines work well. Some people say that the smaller turbocharged engine in the A2 trucks get better fuel mileage. Neither set up will feel overpowered, but they did design these trucks to be abused and survive the treatment that most teenagers will dish out.
So the bottom line is that you (or somebody you trust other than the seller) should give the truck a good inspection. Check for rot/rust. Check to see that it starts well after the truck has been sitting and cooled off. Check the suspension and steering components. Check for leaks on the powertrain and engine. I would even go as far as checking the oil in the differentials, transmission and transfer case for metallic material and/or low oil levels. There is rubber inspection plugs on the backing plates for the brakes. It makes it easy to see if the brakes are in good condition without having to get real invasive removing parts.
They are very easy and fun to drive
And no matter what the internet says, you can get them stuck. I have experience and proof
Anything else, feel free to ask.
Jason