Try to find the spot where the photographer was standing.
The chap standing 1st left looks like Cliff Hay, who was Head of the NSW Premier's Department in the 1920s and early 1930s...he appears in several pics in the NLA's Fairfax Collection...eg - trove.nla.gov.au/work/187281309 ...great Sunday Times caricature of him here trove.nla.gov.au/newspaper/article/128524960
The chap standing 1st right looks like Bill Lush, who was a NSW Public Works Department supervising engineer during the construction of the Sydney Harbour Bridge...we see him 2nd left in this other SRNSW pic - www.flickr.com/photos/state-records-nsw/5578135858
Mr Bradfield of course needs no introduction...
Possibly same occasion [https://www.flickr.com/photos/state-records-nsw/5082075303/]