Hey man,
I did a similar mod to my Tacoma. I put the Premium Scion head unit into my truck, which I believe to be the same mounting and size as the Scion Nav. System. It does take a little bit of modification to get it to fit correctly.
First of all, it is plug and play. All of the Tacoma plugs (Steering wheel controls, etc.) plug right into the Scion unit. I plugged my premium unit in and it worked right from the start.
There was some minor fabrication (or so to speak) to get the head unit to fit. First of all, I bought the Scosche mounting kit for the Tacoma, and modified it to fit the Scion sized stereos:
Then, after I got the mounting kit dremeled, modded, and painted black, I had to modify the brackets for the stereo for them to position the stereo correctly within the bezel. Here is the test fit of the stereo with the mounting kit removed. The stereo actually doesn't mount using the scosche kit, it mounts on its own, unlike the regular Tacoma stereo. The schosche kit is more or less just a stereo surround in this case. Here is a pic of the mounted stereo, then a pic of the stereo with the surround all installed:
So, it can be done, but it does take some work...
On that note...I have since upgraded my stereo to an aftermarket unit, so I am no longer using the schosche mount kit or the original stereo brackets I modified to fit the Scion head unit. If you would be interested, I would sell the mount kit and brackets. I no longer need them nor do I think I will ever use them, they are just sitting in my workshop collecting dust.
Your best bet, if interested, is get on a Scion forum and verify that the two units are the same faceplate size and use the same mounting (which I am pretty sure they are), and then let me know if you are interested in the parts that I have. I just wanted to let you know that it can definately be done.
Hope I could help! Good luck in whatever you choose!
