I ended up using the guide
here. Took me 45 minutes, and that included tracing and removing all the cables for the old Nokia car kit and the iPod adapter. A few trim tools, a Torx T20 and a bit of patience and preparation was all it took. Just be careful as you remove the trim round the head unit - the clips on the back look quite fragile.
Luckily for me, no coding needed for the basics (as I took an MFD2 out) and luckily as well the audio is fine - in fact it's a lot better than the MFD2.
Bound to be a bit of coding this weekend though - not got the track displaying in the dash yet, and there's the small matter of the RSAP Bluetooth kit and MFSW buttons sitting on the table......