Try to find the spot where the photographer was standing.
" In 1883 he [William Henry Paling] bought large premises at 356 George Street for £45,000 and reorganized the [music] business as a limited liability company. In 1891 Paling moved to the company's present  site at 338 George Street. " - from adbonline.anu.edu.au/biogs/A050444b.htm
This building was near the corner of Martin Place (or Moore St as it was), not in The Rocks.
The "Post Office Resumption" notice (see note) was due to the building of the GPO and widening Moore Street into Martin Place, c.1890. The top parapet of the GPO is seen at mid right,
From another angle - www.flickr.com/photos/powerhouse_museum/2363485956/
Google street view - maps.google.com.au/maps?f=q&source=s_q&hl=en&...
Thanks for the info and the links, beachcomberaustralia. Will update our caption!