No, the NMEA2K adapter is a one-way communications gateway. It will convert NMEA2K data to work on the Ethernet system but not allow information to flow the opposite way. You will need to make other connections to get the GPS data from either the 998’s or 1198’s GPS Receiver to the MercMonitor gauges.
Assuming that they will accept NMEA 0183 data sentences: will need to know which set of wire colors your intended GPS receiver has in its NMEA ‘pigtail’ connection wire. This is the shorter second wire that comes out of the connector for the GPS Receiver. They will either be Red, White and Black or Green, White and Black.