6029 is an AD60 class Garratt actually (very few Mallet locomotives ever found their way to Australia, although a small one is in Western Australia undergoing restoration), although it's easy to make the mistake! But yes, she looks and sounds incredible.
You're right on the money with the 40 class being Alco-engined, because it is indeed an Alco! (Intersting is both locomotives symbolize the transition between steam and diesel, the last steam locomotive class and the first diesel class on the NSWGR).
Either way, that is a fantastic video! Thanks for sharing!