I can place train builders and then I can place power poles between them. But if I try it the other way around the power poles are in the way and the train builder can't be placed. I believe this is so the train builders are always build with 1 tile gap when I drag&build them. But this will cause problems with blueprints.
After building the train builder are the size of a locomotive (6 tiles). If they where smaller, say 4 tiles long, then one could place an inserter next to the rail to fuel locomotives. This would remove the need and problems with train fuel recipes and special fuels not working. Probably would also allow a pump for diesel fuel.
