When I came across this clipping several years ago, I did not believe that Mt Druitt actually had a Grace Bros. It was the anchor tenant in "Marketown". In 1992, it would land in the hands of Westfield and become Westfield Mount Druitt.
Source: Grace Bros. 1973. "Mt Druitt Grace Bros Opening Advertisement," The Sydney Morning Herald, October 9, 4.
I had to do a quick scan of the internet to find out a little as to what happened to the store. Going by what I have read, the store closed in 2004. The space is now occupied by Coles and other specialty stores.