There is only a handful of people in Adelaide I would let loose on this. ...and they cost plenty!
I suspect the way forward for you is to get an assessment of what the ole girl is like........worn well and well worn I'd surmise. BUT if you get an estimate of the top 5 items that need attention, you can then decide on whether you want to spend that kind of money or move on. To work your way progressively thru the car to get it reliable and smooth is in the 1000's if you can do it yourself: or 10000's if you have to pay someone to do it.!!
Of course we can all do the basic things ourselves but it's the thorny issues in a 40 year old car that require specialist knowledge and tools.
You may or may not be au fait with the W116...........if so great start..you will need to bring your A game however to the 6.9 aka "bottomless pit"!!!

As a matter of interest how many KMs is she supposed to have done?