What loco would be used to pull a work train on a midwestern, branchline, railroad in the 1940-1949 era?
A ten wheeler, a mogol, or a consolodation would all work.
Also, an older diesel like a boxcab. The RR would assign any available power that was not slated for a higher priority train. That being said, if the work was an emergency repair the first available locomotive could be used just to get the work train to the emergency site and get things rolling again. Work trains were not fast trains; often cars in the consist like big cranes has speed limits because they were not that stable at high speeds.
I do not find any reference to a “box cab” Is it like a NW2?
Boxcabs are deisel switchers where the carbody fully covered the frame with flat front. As in:
http://home.att.net/~Berliner-Ultrasonics/boxcnj1k.html
Boxcabs were typically found in urban areas, a boxcab (other than an interurban/trolley boxcab) would be relatively rare in a midwestern setting.
Basically the work train would be powered with whatever was handy. Assuming the work train is being used locally out of a terminal it would be whatever spare engine that could be assigned. Since a work train is typically small it cold be any size from an 0-4-0 or 44 tonner, up to full size freight engine like a mikado or a decapod. It might be a switcher, it might be the reserve freight or reserve passenger engine. Whatever was handy. Work trains only ran a couple days at a time, very infrequently (maybe a couple times a month).
Dave H.