I am surprised that there is any confusion about who designed the Sidney Harbour Bridge.
I worked at Dorman Long, Middlesbrough, from 1951 to 1956 and at one time I possessed a thick copy (about 50mm) of the Institution's proceedings entitled, The Building of the Sydney Harbour Bridge dated 1934.
The Institution would presumably have a copy of this volume in its archives, which should clear up any doubts about who was responsible for what in the construction.
WE Pearson (M), jopearson@f2s. com