Picture is a bit small even on the larger version and slightly dark, but it appears to be based on an Industrial Brownhoist 250 tonner. A number of these were steam when built around the 1940s but quite few ended up being converted to diesel losing the stack at the back and picking up louvered vents on the rear sides for cooling. This appears to be the diesel version. Looks similar to the Arnold model but it appears to have better rigging to the boom as the Arnold version is minimal. For sure that they were around up into the 1990s since I photographed one on the South Branch Valley in the late 90s. It may also represent a Bucyrus-Erie since it appears to have CN markings. http://www.railpictures.net/viewphoto.php?id=354094
i think it is not too far away from a brownhoist crane. here's the prototype i used to paint my model.
its based on a european prototype diesel crane thats been around in one form or another for as long as i can remember it can be modified to a north american crane with a little styrene and some good photos .
