Bern444, The audio side sounds interesting, so a 120k resistor in series on these leads is enough? You'd think there be a big market for a device like this , if one was available comercially, it would sell like hotcakes
In the interests of science I just took apart the fixed wing adaptor, not having opened it since I made in in 1996 - and yes, it's 120k, with the resistor inside the XLR plug. All the parts are easily and cheaply come by, so unless you're totally ham fisted you don't need a commercial version.
I still don't know why you want a clamp in a PA28. With Jeremy Clarkson in an F15 or James Mays in a U2 you do, because there's no room for anything else, but these days they'll probably mount at least two cameras to give them variety. In a PA28 you have the freedom to get lots of different shots if you have a passenger hold the camera. Watch a normal documentary and you'll rarely see a shot that lasts more than about six seconds because after that it gets boring, and so will your film. Handheld solves all your problems and gives you a much better result. Here's one I made earlier -
YouTube - Piper PA28 Flight from Fairoaks to show you what I mean.
B