Duncan,
That sounds like a good route, so let's pencil that in from Dumfries to Kirkudbright, aiming to get there for 1pm ?. Can you suggest an impossible to miss meeting point in Dumfries or on the road to New Abbey for 12.00 for everyone coming on the run ?. Dumfries or thereabouts would seem to be a logical meeting point for groups coming from any direction.
After Kirkudbright I was thinking of going west to Wigton/Port William then back to Newton Stewart-New Galloway-Thornhill-Elvanfoot. After that the various groups can disperse north, south, east, etc to get home. The days are long and the Galloway roads are stunning and under-rated so it will be a belter of a run - all the better with the Ducati orchestra roaring along !.
If you can get back to me with a meeting point I'll put up the route etc on the calendar.