It will work... definately.... simple plug-&-play.... the only difference is that GPS-antenna should be connected not to the GPS-receiver (like it is with MK2) but directly to the MK3 or MK4..... That's it!

You can find NavTweak here http://www.xoutpost.com/electronics/...-navtweak.html (deeper in that theme you can find the latest version, 2.7 as far as I remember)