This is all great stuff Phil.
I too am modeling the ECML in this era (Welwyn North), but in N gauge. (How I wish an N gauge C1 was available!)
I grew up near Welwy North, was a regular at the Cowper Arms for a while, and commuted from the station in the 1990s. When in the area in July (I live in Massachusetts) I spent most of a day happily photographing and measuring to enable me to draw and build the structures. I had not realised that so much of the coal drops has survived! Currently, I am having a lot of fun researching the beehive works (which I vaguely remember) and reconstructing it on paper.
My project is focused on 1930, but stretches to 1925-35 and beyond. I am in the planning stage at present, slowly collecting and building stock and still a long way from actually constructing the layout--or even figuring out where to house it!
My research is ongoing, but I wonder if you were able to establish the track plan at Welwyn North in 1930? I have a pretty good idea what it was like at that time, but don't know if the crossover in the down sidings seen in early C20th photographs was still in place at that date. It had gone by the mid-30s, and is a feature I would like to approximate using Peco Code 55 track, but it would be much simpler and cheaper if it were not period appropriate!
Many thanks.
Jonathan