Hi Anthony,
Not much response I'm afraid. All I can offer is that the "Allchin" TE design shows a 3-cock gauge which perhaps could be adapted. Hughes went into great detail on building this engine in the ME series, later published as a book, so if you can find this information it would probably be helpful.
I attach a rather poor scan from my elderly set of drawings. Hope this helps

Edited By Clive Brown 1 on 10/03/2021 15:19:17