300 hp G2s with digital controls needs rpm input for auto pilot

[odoodo]

I replaced my 2013 twin 300 hp E-tecs which had mechanical controls with 2018 G2s. They have digital controls - ICON Touch 4.3C and ICON II dual binnacle. My auto pilot has a pair of wires to each motor for an rpm input. It is a 2007 vintage Garmin TR1 Gladiator auto pilot. I think that I need some sort of digital to analog converter. Any ideas what to get and how to hook it up?

[boats.net]

The analog converter is part number 0766287 that will connect to the NMEA 2000 network and provide an analog tach signal.