Help with Chain Transmission Parts on Thos Green LM17

We are a small Mens Shed in Northern Ireland. We have been donated a Thomas Green LM17 approx 1954 to refurbish and display alongside out other mechanical items. We have the owners manual which includes Parts diagrams and also a Villiers manual. Our initial problem is to find or manufacture the assembly which includes the freewheel on the right side of the mower (looking forward from the steering handles) that is outboard of the right side chassis plate. I believe someone in Australia has a concors  quality rebuild and may be able to help with measurement. Nick Rogers, Drumbo Mens Shed 

In particular does the Sturmey Archer (Sun) 13 tooth freewheel fit?