Hey,
excellent trip for a KE70!
I did the trip from Newcastle to Adelaide a dodgy Datto 1600 heaps when I was a kid. Regarding KE70s, I picked up my Grandmother's KE70 in the last couple years. I keep it well serviced. I drove this car 120 kays each way each day when I worked in Sydney. It can handle the speed if you are smart. The KE70 is good car, it just doesn't handle high highway speeds in standard trim. It is a suburban car.
Having said that, if you have a little mechanical sympathy, you can find slower motorists who you slip behind for the long hauls. I found it was best to pick a car travelling at an OK speed and sit three seconds behind them for a couple hours. Your trip will be OK. BTW I drove from the Far North Coast of NSW to Newcastle many, many times in a KE70. It can handle the long trips.
Roh