Just out of curiosity, I know this sounds a stupid question, but are all of PBR's engines (except for the new garrat) of Australian origin/type? The little red stem engine looked American, kind of like the logging engines and some of the other stuff looks almost Toy Train like, like the Darjeeling trains (B class steamers?).
In short, the NA class locomotives are to original (or there abouts) standard as ordered by the VR. With modern day modifications made. Electric Headlights, swing seats, bigger compressor just to name a few, and 6A being fitted with modified front end.
The little red loco, aka John Benn 861, was built by Decaulville in Germany, for the use on the West Melb Gas Works, and looked alot like sister engine Carbon. (search for pics somewhere). 861 was bought by the mob that use to operate at Wahalla back in the day with leading hand, the late Ron Kain. The loco was dressed up to look some what "wild west" american style, but was the orignal 0-4-0 configeration. Was then bought by C.Reese and transfered to PBR where restoration commenced, including adding pony and trail trucks to make it a 2-4-2ST (saddle tank). The decision was made to keep it in the American Style as when it ran at Wahalla. Carbon was kept orignal as a Side Tank 0-4-0.
This is about what I know, many others would have more information on it as well. Hope this helps to anwser your question though.