I saw this chassis listed on the big auction site. It's definitely an SHS product but I can't help but think it's part of a repaint as the chassis shows "SW-12" painted on the edge.
SHS made SW-1, SW-8, SW-9 and NW-2 models in their switch engine line. But never an SW-12 model like this:
There was such an engine in real life in many paint schemes including BN as shown here and I think that's what the modeler was making as the chassis edge looks like the one in this picture:
Too bad the seller doesn't have the complete engine as it would have been nice to see.