The first step is to investigate where these would have been placed and what service they will provide.
My first thoughts are next to signal boxes and station buildings, and any other important buildings such as engine sheds.
The next consideration is the distance most of the line side places would be on straights and curves. Suggestions come in at about 60yd gaps, but I'm working on if it looks right it will be! The most important objective is to make it line of sight from one pole to the next and this might mitigate a regular distance.
There will be situations where the poles cross lines and boxes and cables will possibly be required.
I've identified around 28 sites on the railway where poles would have been in use. below are the buildings that would have connections, (engine sheds, signal boxes, station buildings, huts, etc).
4 in a pack from Hattons at £5 each pack