I believe the Garmin 18X-5hz gps will work out of the box.
BUT, check for proper input voltage, it requires 4 - 5.5 vdc.
Connect the gps #4, white, transmit data, wire to the ADI Pilot II pin 17, Primary Serial Input. Also be sure of a common ground between the gps and the autopilot.
Yes the Garmin gps can be reconfigured if needed. I needed an adapter to connect it to a laptop serial port, and software to read/configure the gps.
The adapter was made by Keyspan, the software came from Garmin.