David Clark H10-40 & -46
A friend has an H10-46, new, with the U-174-U helicopter plug
an H10-40, slightly used with dual plugs + an adapter to a single plug.
According to a document that David Clark just sent me, both headsets are 150 ohms impedance.
If you are interested, I think he will accept $200 for either, shipped to Conus.
Merrill D. Evans