thank you Mike & Aire Head for the replies. Thanks for being patient!
some very useful suggestions and things for me to think about. I like the idea or adjusting the HST timetable to suit weather etc, exactly the kind of thing I'd like to do.
What would help me get my head around the challenge is if you could recommend a resource for 1970s British Rail London area, wagon labels, waybills, train graphs and the documentation that was used to make up passenger trains. Procedures for empty coaching stock trains, and the stuff that happened overnight.