These little Plymouths were such a common sight at so many factories and industrial hubs when I was a kid. This one is one of the larger ones of this design but it is still in such good, original shape. I'm uncertain what is the power now but most were gas engines originally. I know that many were changed over to small diesel engines because of the fuel and maintenance issues. The Diesel Spotters Guide has some good pictures and information on small gas/diesel industrial switchers.
Steve
This one is plugged in so I'm sure it is still in fairly regular use.