My apologies for not taking photos. I meant to -- but then suddenly the thing was together and I was sick of the project and I hadn't taken any photos yet. Doh!
I will be coming back to this when I have a little more time and patience, and will take photos then.
Thanks for all the replies, some very interesting ideas there.
I've been googling and searching for any sign of the Shimano rear wheel dynamo hubs that used to be available, and (just as I thought perhaps I had been hallucinating) I found this:
https://www.amazon.co.uk/SHIMANO-NEX.../dp/B01N554ODJ
