This photo of a Blue Gums concert was taken at the village of Cerisy (Picardy) on 7th April 1919, not at the concert referred to by Jack in the diary entry for 3rd September 1918.
This is a scan of another rather aged negative that shows some of the 43rd Battalion band lads on the Blue Gums stage. The only person I can (almost) positively identify is the corner player seated centre - Sergeant Percival George ALSON.
This photograph appears to be of another Blue Gums concert, of an evening, with nurses also in the audience.
(All scanned from negatives taken by Jack.)