It looks like I can't start a conversation until I have posted more. Would you like to try messaging me? In the meantime, I noticed that you've referenced the website antiaircraft.org.au - but I'm not sure if you've read the chapter on "7th Battalion Recollections and Escapes" which mentions Hall and has the story told from the Australians' perspective ('On Target' - The Book). There is more evidence of Claire-Eliane Engel's acquaintance with Julian Hall in her book A History of Mountaineering in which she writes about his "Escape". I haven't read the book but you can see snippets of some of the JH sections on google books.