I was just about to post details of this on the Norton Owners forum, but thought I would just check to see if I would be doing a duplicate post.
I discovered that My club mate Al Osbourne has been selling something very similar for ages.
If you scroll down this page you will find that he also stocks a very
handy handlebar mount for the 10mm LED. http://www.aoservices.co.uk/data/bsm.htm
He's bringing one for me, to the next meet on Wednesday, so I won't have to make any holes in the Monster to try my widget out.