It is possible to wire 0183 data between the GP1871F and the 1815 radar. This would allow you to share position data to the 1815 radar for data box information. If you send both heading and position to the radar the radar could put out TLL (Target Lat/Lon) to the plotter to mark a location on the plotter. The GP1871F supports receiving 0183 TLL according to the manual. As Kranken said, you will never see a radar on the GP1871F screen unless it is the directly compatible DRS4W.
Dragonfly our IT department said the e-mail you sent them directly isn't something they can assist with. We recommend you speak to your dealer about any pricing questions.