Depends on what you want it to do. If you just want to monitor A/F ratio, then you'll need a bung welded in and some type logging device or WideBand gauge to display the results.
If you want it to track and control the A/F ratio, then that's a different story! You'll need an aftermarket ECM like FAST, BS3, etc. or a Translator Gen II or Translator Pro. The latter two being piggyback devices that can take control of the stock ECM.