For the sake of anyone who is planning on doing the same I thought I'd post to let you know how it has all gone.
I ordered a bracket (Standard II) from the Gadget Guy web site which mounts perfectly. The only issue is that it has cost nearly twice the value of the bracket in postage to get it from the US. I think you could easily get it made cheaper here.
I also ordered the Touratech mounting plate. They lost my order somewhere in Germany but express mailed it to me when I chased it so not too bad. You cannot tell from the web but there is a way of permanently attaching the accesory lead to power it from the battery. This will have to wait as I want to ride the bike now.
The result is a system that fits together with no clearance (and I mean none!). A few knuckles were skinned when fitting but I am a ham fisted fool. The Touratech bracket in particular was quite fiddly with very small aircraft type nuts and bolts. It took a while to work out how to get it all on as some bolt heads are obscured by other parts.
It looks good and the Garmin Quest fits neatly above the yoke. None of the clocks are obscured although it does require you to look down to see what is going on. I do have a little trouble locking and unlocking the Touratech bracket as the lock is very close to the left handle bar. I have to keep the key on a ring on it's own.
All in all I'm happy. Off to Mugello soon so that should sort out any gremlins.
