Wikipedia gives 1500 miles (2400km) for the DC-3A; other sources give 1847 nm/2125miles/ 3420km but there is a very wide range of numbers from just over 1000 miles to 2400 miles
2100 miles may be max.fuel
Melbourne Auckland is around 1630 miles (2625 kms) so I expect there was a technical stop or it was a max fuel trip
various mods could change things - I can remember a DC-3 on airborne survey work with two large internal tanks and an endurance of 12+ hours - approx. 2160 nm ....... and a very nasty experience TBH