I used LEDs in mine. I just used the existing lenses that a part of the shell. I didn't light up the red marker lights though. You are going to need a decoder that will have six function outputs for lighting.
Will
I am modelling a p-42 Amtrak with one engine in the reverse position at the rear of the train and one facing forward at the front of the train. Does anyone know what size bulbs would fit in the holes for the red lights and also the ditch lights? I will be turning these into DCC. The engines are athearn blue box. Thanks, Chris