The Australian tour of the Flying Scotsman took place in 1988, to coincide with the Australian Bicentennial. I remember one day in 1988 waiting on the suburban platform at Petersham station, when I heard a steam locomotive with a slightly different beat to what I was used to hearing and sure enough, it was the "Flying Scotsman" with a train of NSWGR carriages (not the first time I had heard a Gresley pacific in action though - I had witnessed "Union of South Africa in action around Dundee and thereabouts several times in the mid 1970s).
The model predates the Australian tour by at least 20 years. It is, as was stated earlier, a Trix model and not the Tri-ang one and is from the mid 1960s. I'm no expert on Trix, so I won't try to be too precise, but the second tender was added to the real thing in 1966, so the double tender Trix model can't be earlier than that. I have a single tender version of it, which I picked up a few years ago for around £50.00 plus postage - I can't remember what the charge for postage was, but it was unusually low for an eBay purchase.
If you put it next to a Tri-ang example, you will see that the Trix version is slightly smaller. Trix built most of their British models to a rather elastic scale somewhere between H0 and 00, which is usually said to be 3.8mm to the foot, although it does vary.