Thanks so much to Aaron and Jonny for your replies.
And to Sead......your're a champion!
Those photos are perfect.
I have done some rough working drawings to have the nut reproduced, and an engineering firm will run the job in about a weeks time.
Now those photos from Sead will mean an accurate replica is produced. I have opted to have it made in brass at extra expense, so no plating, or rust.
If there are any owners interested in acquiring a part that is NLA,I Have ordered 6 units produced,so 5 available.
If not, I'll only do one.
Thanks again guys,
Mike.