I thought I'd report back on this topic.
With no other option appearing I decided to go for the Universal Rack sold by a couple of ebay dealers.
It cost £46 including carriage and arrived well wrapped and packaged.
It consisted of a pair of twin tube side rails and a separate rack section finished in matt black paint or powder. I can't tell which.
When I removed the grab rail and offered it up to the bike I was pleasantly surprised as it fitted better than I could possibly have hoped for.
All I had to do was to file a little metal from the front brackets to clear the rear dampers and make up some alloy spacers an a stainless steel drop plate.
The only modification I had to make to any of the Honda parts was to extend the indicator wires as the indicators are mounted further back now.
In fact, rather than just splice in some extra cable, I stripped the indicators down and replaced the original wire with a new longer piece. While I was in there I also fitted a proper earth wire too. Honda use a weird system where the grab handle is earthed by two separate wires from an earth lead in the harness under the seat. There is also an internal earth inside the indicator connecting the bulb holder to the metal body. They then rely on the securing screw on the indicator stalk to maintain continuity to the grab handle. I just ran a long wire directly from the bulb holder to the harness earth connector.
I did the same with the front indicators too as Honda originally used a similar system at the front with earthing points inside the headlamp to earth the headlamp brackets.
