Trimble 250 with coverage logging cable to a relay driven from the raven harness.  Or go with a Trimble 750 if you ever want to move up to automatic section control (Field IQ) or steering with more than WAAS.

I started with a 250 connected to my Raven 440 doing coverage mapping automatically.  Works really well to see where you've sprayed, but technology is addictive and after a year doing that, you'll wish you went to a 750 or FMX so you can use Field IQ to automatically control the booms and rate.