If anyone is interested I’m planning a trip over Easter - it will (as far as google earth shows) an easy river as far as no rapids although possible log jams and possibly (hopefully) quite fast water. The basics are 20 to 30km walk along disused road (read no longer passable by vehicles due to neglect) followed by 10km of shallow river in lightly populated area then 60 km thru remote area (there is a hamlet half way) and then thru relatively well populated area to the coast for maybe another 50km. Then public transport back to port moresby.
This trip would suit anyone who is confident in navigating bush in remote areas (in case it’s necessary to walk out) and due to the initial walk not suitable for females (for safety reasons).