Two developments. I managed to acquire copies of Archive, the quarterly journal for British Industrial and transport history, issues 15 and 16, with a full description of a visit to Longhedge in 1903, with pictures of interiors and exteriors of erecting shop, turnery, boiler shop, woodworking shop, carriage repair shop etc.
I also talked with a friend who works out of Stewarts Lane depot on Clan Line / Belmpnd Pullman, who told me there are many relics of Longhedge that survived demolition; he will send me photos when possible.
I have been working out with members of Croydon Model Railway Society how to build, motorise and control the traversers that operated inside the erecting shop and outside the carriage works. It seems the best parts for smooth running and accuracy are the guide bars and threaded rod from a 3-d printer, which someone has available.
I will post photos when I have more to show. Baseboard size will be 1400 x 1200 cm, so its a question of what track and buildings will fit into that.