I think I can safely say that that’s definitely a modified Athearn Hustler switcher. The original owner cut the hood down by about 1/3rd, and did an excellent job of filling in the gaps and cleaning it up! The headlight, exhaust stack, and bell are all steam engine parts, and the drive is the original NWSL “Flea”, but the rest is 100% Athearn. Those 6 holes in the bottom of the frame are where the motor and idler pulleys (for the famous rubber-band drive) were once mounted.
If you scroll about half-way down this page, you can see a small gallery of my own modified Athearn Hustler. Comparing the two, you’ll notice the cab, chassis, walkway, pilots, and many other parts are identicle. These are fun to work on, and you’ve really picked up a nice piece of good modeling work there![:D]