It appears that the "Blacksmith Car" is a myth created by the movie Union Pacific, which included such a car in their railroad equipment, that car having been built by the studio from a former Virginia and Truckee box car.
That car was later offered as a HO model by Trains Miniature, now under control of Walthers. The car as modeled carried a brick blacksmith's forge, with a large bellows, as well as a small hand cranked derick. The blacksmith's work area took up almost half the car, leaving the rest for barrels and such. The reality was much more likely a portable iron forge with a Champion hand cranked blower, which would have been commercially available, and easily set up next to the repair car. Such a forge (large enough to straighten a truss rod) and associated tools and equipment will fit in the back of a small pick-up truck (I did for a car repair/restoration at Railfair 99 in Sacramento). The forge can be carried by two men. We have a photo of such a forge on the SP in Oregon, being used for car repair.
The description of a "one man crew" would suggest that the repairs in place would more likely be light work, replacing a journal bearing, repairing a brake beam or rod, but with one man would not include a wheel set. A wheel set is too heavy for one man to handle, and if an axle failed on the road, would likely call for a wreck train with a heavier derrick, with multiple men and supply of trucks and wheel sets.
The concept of a Blacksmith car makes the most sense if the car and crew was responsible for tool maintenance during construction, not car repair. But it is more likely that a railroad under construction would just send light tools (shovels, rock drills, pinch bars) back to the first division point and shop where they could do the work in a better equipped permanent facility.
With all that being said I have one of the model blacksmith cars...