Interesting.
I visited the Polish 600 mm railways a few times in the late 1970-ties, when steam still reigned.
There they had quite a lot of concrete ties. Although there was some kind of resilience pads between the rail and the tie, I remember it was very noisy and uncomfortable to ride over these "modernized" stretches.
Talking about Australian ties, we bought a load of Australian Eucalyptus/Jarrah ties in the mid 80-ties. They are still in reasonable good shape. But we never repeated it, went back to creosote impregnated spruce ties instead. Except for the extension of the line (between Läggesta and Taxinge) were we could "borrow" a full (std. gauge) train load of used European beech wood ties from the Swedish national rail. Borrowing means that we can return them for destruction when we take them out of the track.
There is an ongoing debate within the European Union on the use of creosote. They want to ban it totally, but it would be a catastrophe for all preserved railways. And no one has been able to prove them to be a real environmental hazard when used in the track.
What kind of ties and impregnation do you use on WW&F?