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I was thinking the same question. I could only find C++ implementation at https://github.com/ttlappalainen/NMEA2000 which I assume you have found as well.

Yes. And that ttlappalainen project generally inherits from the CANBoat project.

Different project, but maybe this helps.

NMEA2000 is the marine electronics flavored J1939. Everything but the data dictionary is J1939.

You can just switch on the J1939 protocol in WireShark.