Matt, "MJNCAD" asked me to start a new thread about this when I brought it up in another thread.
Before the 2305 I had a John Deere 345 GT. It was well modified including some additional electronics to monitor speed, engine temp, RPM, time, ambient temp, and a few other things.
Trailtech makes onboard computers for ATV's and Motorcycle's.
They offer all kinds of sensor options for speed and coolant temp including aircooled sensor options.
So I bought one and adapted it to my 345. I chose an inline hose option for the coolant sensor which worked great except the only "easy" way to get the sensor installed is by putting it in the coolant line on the outlet side of radiator which is less than ideal. The Speedo was ran by a magnetic pickup with a simple magnet attached with epoxy to the rear axle. The engine speed works using a simple wire wrapped around a spark plug wire.
The unit was weatherproof and added some nice functions.
Here are a few pictures.