Don't worry about matching impedances. The headset output impedance is
so low compared to the input impedance of the camera that there will be
no need to match them.

I did this with a JVC VHS Camcorder about 12 years ago & got a good
signal level match with just a direct connection. Just open the
intercom squelch if you want to get aircraft background noise too. You
may have to fool with the signal levels some, but as I remember it
worked out surprisingly well right out of my soldering iron.

I saved the tape as being a flight breakfast example for any future
grandkids.