Thanks Anon; but this is strictly a writing project!
And thanks davecurnock for a good starting point. The Vinten F.24 was originally fitted to the FR.9 and since your reply I’ve subsequently found out that it was replaced by the Vinten F.95 Framing camera, which proved a great success and later went on to be used in the Swift FR.5 and the Hunter FR.10

Anyone who’s got anything to add to the FR.9 story please post, including photos.