Check out the SoundStorm SSV-TS20 from soundstormlabs.com. Looks strikingly similar to my tv tuner, but only 1/10th the cost.
Don't forget to add the diversity antennas. I run just one (out of four included in the kit) behind the cyclops access door, and reception is spotty to useless in the suburbs but excellent in the cities (and the flatlands of kansas, too). Finally, a reminder that the kit I used will let you convert the nav screen to be another video output while still supporting the rear display, and take up to 3 additional a/v inputs (including a backup camera). Oh, and don't forget generator's project to pump composite video out to the nav screen, either. You have a number of options here.
Sorry.. that's soundstormlab.com, not soundstormlabs. I really don't have a clue on how to convert a non-nav to a nav. Since you have specific led segments and icons that are lit up based on events and we nav'ers just have a small lcd screen, there's a world of difference there. if someone was to sit down and parse all of the signals that go into your screen at an electrical level, i'm sure you would be able to hack together a pc interface that simply replicates the non-lcd screen you would be replacing.. but that would be a LOOOOONG way around just to put an LCD display up front. You'd probably get there quicker by installing a 7" flip-up screen in the wide open space available on the dashboard and run your tv/dvd/carputer on it instead. Having had the space around the screen (and the screen itself) and the stereo removed, I can say it doesn't look like there's much of anything under the virtual prairieland up front, making it easy to drill and run wires through. The trick would be color matching a nice ultra-thin flip-up screen to the dashboard.