Thank God for ignorance!
My bike knowledge is very limited. In general I know what I need to build up the bike but not specifics. If I had known this stuff last weekend I would now be broke, having spent loads of money at Mildenhall. As it is, I only purchased a new black Shimano hub dynamo (HB-C050-D) for a tenner. Not the latest and greatest, but it will do. I really was expecting to get a silver one, so now I'll need a black rear hub and black spokes...
I've had a reply from Mercian about the frame. As stated upthread, I was informed that there was a £10 fee (but they did confirm it's from 1982). I'll do it as some point.
As promised, here are pictures of the frame and forks in their current state.
As you can see it needs a bit of work.