I have copy of the book. Page 57 shows a picture of a No. 5 with a square cut .7.62mm magazine identifyed as an XIIE1 and a picture of a No. 5 with Sterling conversion. While my Germanis non existant--I find no further information other than a notation to its existence??? in the accompanying main body text.
The book is an 180 page outline of Skennerton's books in German. Nice pictures.
To stir the pot further, I have handled in Canadaa No.5 made up in 7.62mm using a No.1 MkVI receiver that was purported to be one run up by Long Branch for an evaluation. I do trust the source.