This thing was probably out of service with the coming of the M-420Bs. It was converted from an SP&S FB-1. I really like the smokestack. There must be a stove in there!
None of the units had an "F" on either end (Some wierd Canadian thing?) but his end has a pilot, marker lights and a bell. That says "front" to me. Very likely the only RS-10 I ever saw.