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Yes a diversion is very possible. Drug runners don't necessarily need to start in Australia. Any aircraft from S/E Asia will do. A one-way trip through the North or West of PNG, into Australia, on arrival, unload the goodies and then torch the aircraft. The northern coast of PNG would be the most likely, flying through the West via Papua has its own inherent dangers, namely a forced landing or being arrested etc. The Indo/Papua para military are very unpleasant people and any court appearance would tend to be very brief and the end result unpleasant. I warn all my friends when travelling through S/E Asia, especially Malaysia the most important three words you need to remember is: Barlow and Chambers.
Jindalee; The horizon radar located in the Northern Territory, is outdated and requires enhancements. That's assuming it is on-line 24/7.
The Jindalee Operational Radar Network Phase 6 Upgrade : Department of Defence
The choice of Bulolo is interesting, and actually makes sense. A large expat community involved in Forestry, Crops, Food, Timber, Hydo scheme and Mining and an active and awesome Golf Club. A white face, even a stranger would not attract attention.
The Chinaman arrested at Nadzab about to board an aircraft for Australia; like wise a large number of Chinese owned or operated Trade stores. Construction workers and so forth. A Toyota open tray vehicle is nothing new and fuel drums in the back could be anything from motor spirits, avgas, diesel, Kerosene etc; again not an attention grabber. Risky drive up the highway from Lae to bring in the fuel; but this is a risky venture anyways. There has been a lot of civil unrest in Bulolo of late diverting the police away "other" activities. I can see why they chose Bulolo.
All this adds up to a few expendable people being caught; and a much larger organisation, sitting, watching, and learning.