Not sure exactly what you're trying to do with the railings. If you've made it into a B-unit, you'll need handrails past the area where the cab used to be. I did some modifications to an older Atlas RS-3, which involved adding some battery boxes on the walkway in front of the cab. I modified the stock plastic handrails (not my favourite material for handrails anyway) by cutting out the handrail part (I did all of the handrails, not just the part that needed to be modified), then drilling out the individual stanchions to accept new handrails bent up from steel music wire. Just thread the stanchions onto the wire, then reinstall them on the unit. For your model, you'll probably require a couple extra stanchions on each side, to support the railing in the area where the cab used to be. I'm not sure if you can order those handrails as a separate item: you may have to find another manufacturer that makes something similar, then modify them to suit. You could also try making the stanchions from brass wire; use a hammer to flatten one end, so that it's easier to wrap around the handrail. Utah Pacific made brass handrail stanchions at one time, although I don't know if these are still available.
Wayne