One of our Aussie friends can correct me if I'm wrong on this, but I believe that at this point (with the large center bolt/fitting removed) that it's just being held in there by the gasket/sealer- work around the edge with a hammer and brass drift and it should pop loose... looks like it's attached the same way a U.S. 90* filter adapter is held in place- just by the large center bolt, which you've already taken out. A couple of firm raps with a rubber hammer usually knocks those loose.
Then you can clock the pesky fitting any direction out of your way and re use the base.
Since it mounts in a similar fashion, I am guessing you will need the gasket set for a 90* filter adapter when you reinstall.