PC-6.com says it was used to rebuild s/n 551 (Astazou and then PT6 turbine Porter) which matches Tail Wheel's memory.
PC-6 History s/n 660
They also list a dozen or so piston Porters registered to Merpati, including a couple photos of two sitting in the grass at Sentani. Presumably it was one of their Porters in your photo.
Curious about the Australian MTOW. From Pilatus' training material, the H2 variant is 2200 kg (4850 lb) MTOW [and I think 2600 kg MTOW for spraying/water bombing] and the H4 is 2800 kg (6173 lb). Are you saying a B2-H4 only has a 4850 lb MTOW in Australia? Or they just won't allow anyone to operate the H2 overweight?