The long haul headsets were probably the old Airmed Airlite 62. Also used on the Britannia and still being made today. Astrolites came in a number of configurations, either with or without a (carbon level) amplified microphone. Those with the amplifier would likely have been more readily suited to other civil aircraft radios, such as the Cherokee. They also work nicely with the David Clark intercom systems fitted to many deicing vehicles! Better than the head-squashing green domes!!