David, many thanks, that's solved the puzzle over how GWR had fitted that many sidings into the space south of the station.
On the older map, south of the station building, there was a triangle of ground with trees, which I'd assumed was the limit.
From your general plan, it's now obvious it has been used to both extend the sidings and reduce their curvature. Here's my "Mark 3" attempt, using the extra space, along with a goods shed, the station building, footbridge and a signal box.