It is a TomTom GO 6200 Wi-Fi, model 4PL60, I don't think it is still available. I did this conversion four years ago, it has worked perfectly all that time. It has wifi so it updates the maps automatically. I posted a picture of the dimensions of the original satnav screen in case anyone wants to do this with a current satnav. The unit is stuck to the inside of the bezel with Sugru and has a thin sheet of padding between it and the original satnav circuit board. The Sugru has held for four years, I have used it for other purposes and am sure it will come of cleanly when the time comes.
It integrates with my phone for calls and messages but not with the Lexus system and controls.