Ok folks, here is the final install on this Speedo Post. Here is what I ordered from a popular online site:
Samdo 85mm SOG COG ODO TRIP Meter
The reasons for choosing this model was that it would fit the existing hole in the panel, and that it was GPS powered which avoided the need to re-calibrate after installing my 3.07 gear-sets. It also had a non-resettable odo, a trip odo that re-sets at each power down, and a compass direction indicator. I believe these were made for sailboats, and it offered an easy change from miles to Km via a small button on the back.
The big test was driving to Overland Expo. The unit was easy to install and there were only three wires to power it, plus the small cable to the GPS Antenna. One wire for Batt +, one for ground and one for the back light. I taped into the existing speedo wires for what was needed and powered it up. The display is easy to read and the back-light worked great at night.
I ran this side by side with my Garmin 600 Montana for the duration of the trip. I did notice a slight error on the Samdo unit which I attributed to the temporary antenna placement.
Overall, pretty happy with the setup and can recommend it if you are looking for an easy replacement.
Pointman