Both the Commonwealth Railways and the NSWGR operated Budd type railcars.
The Commonwealth Railways imported three from the US in 1951 while Commonwealth Engineering built five for the NSWGR.
The first for NSW entered service in 1961.
In the US these self-propelled railcars (known as RDC’s) were quite popular with east coast and Canadian railways
Models of similar railcars operated in the US have been scarce for some time and about the only one in HO that I remember seeing was produced by Athearn and featured a rubber band drive.
But now Rapido Trains Inc are about to release a brand new version of the RDC and you will see the finished product in this video.
While it’s not an exact model of the NSW Budd Railcars it may be a good starting point.
It’s definitely worth watching. Even though the video mostly deals with the model you will see, and hear it, running on a great layout.