Thank you for the deep dive on the history of these communication protocols. There's a lot of good information there, though there are a couple of errors I feel I should correct. NMEA2000 is not Ethernet-based, it is CAN-based. The consequence of this is NMEA2000 has its own standardized round connectors, not the familiar RJ45 connectors most people know from their home internet router. To my knowledge, there is no industry standard Ethernet solution for marine instruments, though there is one under development called OneNet. Raymarine's proprietary SeaTalkNG is their NMEA2000 extension, and SeaTalkHS/RayNet is their Ethernet technology.
My reading of the Airmar 220WX specification sheet
says it supports both NMEA0183 and NMEA2000, so Duane should have plenty of options for interfacing. I'd recommend NMEA2000 because it's the more modern standard and can have multiple devices on the same bus (cable). That same document lists a bunch of heading information that comes from the unit, so I think it would suffice for the radar on a technical level (this could be confirmed by comparing the needed data messages in the radar manual to the output messages of the 220WX), though practically might have error introduced by being at the top of the mast.
SM 233 Iteration
Boston, MA, USA