Thanks for the comments. All good points.
I'll probably press forward with this if I can find an economical way to connect these couplers that I have. I'd love to do it the standard way with metal pipe but frankly it sounds expensive, and I don't have the tools or the time right now. I have all kinds of PEX and fittings laying around and a crimper and cutter.
If water, or oil, or temperature, or any other variable compromises my system, well then I'll have to redo it with metal at that time. Not a huge deal. Probably be in a better position for that later anyway.
Kultuz, there is nothing wrong with that drop ear, except that the air couplings I have are female. If I have to do it with two fittings, so be it.