Assuming you have a touch screen radio already an RBZ? If you want the factory in dash NAV unit you'll want to look for a high speed RHB radio or RHR. Keep in mind that the back light behind the hard keys will be a different color, not red unless it comes from a Routan already. Look on Ebay for and RHB or RHR radio. I'm sure some others will chime in as a few guys have just gone thru this. There is also no input to the radio other than the USB for file transfer and iPod integration, and the 3.5mm aux input so I don't think it's possible to use and aftermarket dash mounted GPS and output the data to the screen on your radio, if that's what your asking.
Here's a few links: