Trucks like you are talking about do exist. Most were custom are for highway departments and rusted out due to the salt spread on the roads. If you can find the remains of one and transplant the mechanical parts onto a truck with a good frame and body, you would have what you're looking for. I would start checking junk yards to see what's there.
How about the GM military trucks from the late 40's, certainly narrow axles and appropriate size or weight capacity compared to later military stuff. How easy would an AD cab replace the 40's cab? Or again just use whichever truck as it is.
Grigg, you bring up a couple of good points. The WW2 G506 Chevy drivetrain has axles that are quite narrow, and could work under an AD cab. I would hate to see some rare driveline parts being consumed in an a non-g506 application though! Another good donor would be the later m-211 or m-135 Korean war GMC 2 1/2 ton truck. These models have the same axle width as a WW2 Chevy but include some technological upgrades. The best part with the M-211/135 is that most of them were built with an automatic transmission that is an Achilles heel for that model leading to most being sent to the great scrapyard in the sky. Complete dead transmission M-211/135's can be found for under $2000. Gear ratio is 6.67 for the Chevy and 6.17 for the GMC so don't plan on getting anywhere fast.