Thanks for the advice guys!
Will look more closely at the Tom Tom Rider and Garmin Zumo, but I think I will need one that accepts a remote GPS antenna, as my M3W has the updated gear lever, and the sat nav will be hidden well under the dash.
In fact, I doubt I will get to see the screen very easily, as the steering wheel and gear stick will obstruct it. Will be more reliant on verbal instructions through the intercom or

. Will make a change from SLOW DOWN! Who at Morgan was responsible for putting the speedo directly in front of the passenger