Hi Mitchell – nice “find” mate.
I wonder whether this is an azalea or one of the other 6 Rhododendron species (I think there are 8 from memory). Do you have a close up of either flower or leaves (before its haircut

)
Not sure where you are in Sydney but I have seen some of these in the older areas of the northern suburbs and they are spectacular.
Either way it’s going to be a really nice tree.
I think to get the best out of this it is going to need some more surgery as others have suggested.
Something to think about might be whether you take a couple of years to trim it back. From my experience if it is done in one hit, you have a fair chance that all roots will survive – equally you have a fair chance that some of the roots will die back – which means you get dead section on the lower trunk.
Another option might be to cut it back some more and allow some stubs to grow for a year or so all around it. This may help the root ball survive, in which case you can give the final haircut in a year or two.
No matter your final decision, I look forward to the progression.
Regards
Steve