@ScoutingDad,
I finished my LED project on my Dash8-40B. The first picture at the bottom shows the inside work before I zipped it up. Note the green shrink tubing on the two sides. The ends are 3 mm warm white LEDs. They do a good job of lighting up the number boards (they're right behind them), and I didn't mask off the light going inside since it was the light need for the cab interior. Note that I cut a strip of 3m double sided heavy mounting tape to fit inside the pillar. I pressed the shrink wrap tubing against that tape and it seems to be holding well. You can barely see it from the outside. Now note the orange arrow. It is pointing to two 5 mm cool white LEDs placed side by side, and the shrink tubing is keeping them close together, right behind the headlight lenses, and they look great. I did mask the light from these bulbs going into the cabin because it would have been too much. Again I used double sided 3m tape cut to fit the pillar and hold the shrink tubing. If I had to do it again, I would use 3 mm cool whit bulbs, which would make the end of the shrink tubing behind the headlights smaller. You can see this wire a little bit from the outside, but oh well. I did not glue any of the bulbs in place. I hope the 3m tape will keep them from moving.
Update: The partially exposed wire for the headlights is too annoying. Since I didn't glue them to the lens, and the wiring now is not bad to deal with, I will be replacing them with two 3 mm, although I don't know if I have any cool whites in my supply. If not, it might be a few days. I'll update the pic then.
Note the little person with one leg hanging. I glued this engineer figure to the side since there was nothing there. I cut off his right leg so as to not potentially interfere with the motor movement.
The blue tape is on top of the factory black tape to mask off the flashing light from the inside. The strange looking thing on the far left of the pic is a bulkhead I made so as to not be able to see the entire inside from the front of the engine. I painted it black and pasted on some pictures of equipment of what might be inside a diesel. I think it looks way better than what I got from the factory
I removed the incandescent bulb from the front, and used the power going into that to drive my 4 LEDs (wired in parallel). I still kept the grain of wheat bulb for the flashing bulb on top, and didn't replace the light bulb in the back. I did doctor the bulb holder a bit to remove some stuff blocking the light output.
I attached short videos showing the outside of the front cabin close up, and one of it coming down the track.