Hi Willem,
congratulations with your beautifull mandau.
A very nicely carved handle, scabbard and belthook!
But......I don't agree with you this is a mandau from the Mendalam dayaks.
I more think it would be from Bahau's living in the area of the upper Mahakam.......
But it would be nice to discuss it with you, as I could be wrong here.
I based my hypothesis on typically Mendalam characteristics that I miss in your mandau....
So.. I vote for Kayan, upper Mahakam..
Vr. groeten,
Maurice