I have done that one a few times. The first time we had to change trains about halfway, in Albury. The railway gauge in Victoria, wherein is Melbourne, was wider than in New South Wales (Sydney). Different now thankfully. A few more times in a train called the Spirit of Progress. A misnomer if ever there was one. Cold, old and uncomfortable.
There was another train, at least back then, which I think was more luxurious. The Southern Aurora. Sleepers I recall, though I never did get to experience it. I suspect my employers were too tight to pay.