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That's a very attractive machine!
The brakes - do they work in the rain?
I have ridden a bike with a similar (probably identical) derailleur. It did change, but I couldn't get it to work well, probably my fault, but it did seem disappointing. That long arm should give scope for a small inner chain ring, which might make the bike a practical tourer without doing away with the three speed block.
Before you bother with a hub dynamo, get hold of one and try turning it by hand - I think you will find there's quite a lot of resistance, and that's there all the time whether the lights are on or not. Then there's the weight to consider.
The top sprocket looks a bit worn. If it's any good to you I have got what I believe to be a French threaded 3 speed block. You are welcome to have it, if you want to come and collect it from London NW10.
That front brake it quite a piece of work!