Here are two knives that resemble the description and line drawing of a Sulawesi bangkung in Albert van Zonneveld's book. The beaten up, lower example came from a GI who served in the Second World War and saw action in the Celebes.
It does seem true that the word bangkung refers to somewhat medium-sized blades among the Bugis and other peoples from SW Sulawesi - I'm not sure if I really grasp the native definition(s) though? Could it possibly be a fairly broad/generic term resembling golok/bolo?
Like Detlef, I also hesitate to attribute these 2 examples to Sulawesi Selatan. Did this GI also "visit" other places throughout the archipelago, Ian?
It is possible that we do see some Bugis (in a wide sense) cultural influence here - it may be indirect though...