There was indeed a C421 (a B-model as I recall, and also originally registered as P2-PNG) that gave way to the B-200 P2-PNG.
When the G-II arrived it became P2-PNG and the Kingair was rebranded as PNH.
The G-II had a short career in PNG, and was eventually sold somewhere in northern Europe. It became something of a political football, as I think Sir Julius bought it, but Sir Michael disposed of it (may have been the other way around).
No doubt when the dust settles and PNG returns to having only one Prime Minister (as opposed to 2 at present), it will be time to "review" the fleet again!