Can the GP1871F GP1971F Combo units be connected to, and share the data with, a TZT or TZT2 MFD over an Ethernet network

​No. The GP1871F/GP1971F Combo units do not have a wired Ethernet port. The combo units can be connected with sensors via NMEA0183, NMEA2000 for data in/out, as well as connected to the DRS4W radar sensor via a Wi-Fi LAN connection. They can also be connected to the same NMEA2000 bus as a TZtouch or TZtouch2 MFD and share NMEA2000 data with those MFDs.