This is an old engine without the LED lights, flywheels, low friction trucks, or Micro-Trains ready coupler pockets that we have become accustomed to. At about the time DCC started to catch on with N scalers in the early 1990's, this was a very common mechanism that was used on several models made for Atlas by Kato in the mid to late 1980's. They do have a good motor, and with a DCC decoder momentum can be programmed to help make up for the lack of flywheels.
First step is to take the engine apart. Getting the shell off is the hardest part. Here's the trick. First remove the cab to expose the catches that hold the shell to the frame.
Once the cab is off, the main part of the shell can be easily removed as shown in this photo.
This photo shows all of the parts after this RS11 has been dis-assembled.
This mechanism is almost identical for the Kato made Atlas RS3, RS11, RSD4/5, RSD12, GP7, and GP9.
Here are the lengths that I cut the decoder wires to.
2" - White
1-7/8" - Red & Black
1-3/4" - Orange
1-1/4" - Gray
7/8" - Yellow & Blue
This photo shows the decoder wires solder to the modified light boards and the motor brush caps.
The next two photos show the details of the light boards.
The PC boards are the same as the common Kato 77A board. It's just that these have a light bulb and a diode instead of a LED and resistor. The directional lighting will be determined by the decoder so the diodes are not needed.
The red and black wires from the decoder will make their connection to the frame from this board.
On the rear light board I cut off the tabs with a Dermal tool, removed the diode and soldered the blue and yellow wires from the decoder to the light. Polarity will not matter with the light bulb. A second blue wire was run between this board and the front board.
Re-install the brush caps with the brushes and springs on the motor. Then place the motor assembly into the left side frame as shown in this photo. This one did not have any separate worm gears or bushings, it was all attached to the motor.
Here is the completed DCC mechanism. As you can see, there is lots of room for the decoder. Any of the small wired N or Z scale decoders could fit in this space.
These older engines had truck mounted Rapido couplers with big openings on the pilots.
Micro-Trains made pilot conversion kits and these are still available. For the RS11 look for Micro-Trains part number 1150.