If you're asking how to add GPS, you need a Trimble Universal receiver package or equivalent. Been several years. They were around four grand. Have no idea now.
I have a 1688 with the older Case yield monitor that was built, I believe, by agleader. I have an Agleader 1000 beacon. Seems to work fine. I'd sell it so I can replace it with a higher frequency beacon for a lightbar system. Email me if you are interested.