Remember that they have to shovel coal from the coal car to the engine so there would probably be a platform extending out over the coupling and therefore not too much gap between the two cars. There would also be a ladder/stair up the front of the coal car from the engine to access the top of the coal for shovelling, and probably at the back of the car to get to the rest of the train. There are generally stair/ladder type things at the front of the walkways too, but you have an armoured cow-catcher it looks like, so it may be different. Generally there are also handrails along the walkways so some hapless engineer doesn't fall off the train, even when its not moving it's quite a fall. Looks like its going to be a pretty cool project.