I saw these a while back on the Discovery channel. They also built a small one on a quad bike chassis that I thought was pretty cool.
I think that Aussie one is built using a WW2 Stuart Tank as a donor for the running gear. Have a look at the track setup on the pic below.
On a somewhat related topic a few years back a mate of mine changed jobs and now does maintenance on Australia's M1 Abrams fleet. We all thought he was pretty cool when he got his license to drive one and was driving them around at work. Lucky Bugger.
Cheers