I was wondering if the car could have been in foreign service at the time of the photo. And perhaps it was. But as I noted in my just submitted comments, the tank looks to me to be in "pre-release" form. Thus it would be unlikely to be out of the country.
Getting a tank on and off a depressed center car is MUCH less fun than a standard flat. But if one needed better vertical clearance, say in Europe, it might be a good idea. But that raises the question of European weight limits and axle loadings. Total weight for a depressed center car is usually higher than for an equivalent load/flat deck car.
I note that the ORER says of the USAX reporting marks: "See Department of the Army, Transportation Supply and Maintenance Command". If the subject car were "owned" by Army Ordnance, it would reasonably not be listed by DOA,TSMC.
I find the number series interesting. At the time, only NYC used the 49xxxx numbering. Yikes, what are the odds?