Thanks for all the advice guys. You've convinced me to keep it all-original as much as possible. TBH, even if I do end up changing the mudguards for example, I'll hold on to the originals so I can always put the bike back to stock.

I'll go ahead and try OA and maybe vinegar on the rusted steel parts. Just to clarify, am I safe to use it all the metal parts of the bike, or are there any parts (brake calipers, levers...) which are not made of steel?

Would it also be OK to use OA on the painted frame surface rust?

I agree that it's strange that the original owner seems to have specified everything except the rack to make it a Superbe. Can't imagine it would've been cheaper that way, but I guess we'll never know...

The cables seem to be OK, but at least one of them is not original - the front brake cable has a nut-and-bolt clamping arrangement rather than the fixed end (what's that called?). They are also pretty much at the end of their adjustments, so are correct-spec replacements available, or is that the reason for the front brake make-do?

What's the deal with the "3 or 4 speed" trigger? I'm fairly certain that mine's a 3-speed, although that leads me on to the next question. In order to ship the bike to me, the guy I bought the bike from disconnected the cable by unscrewing it from the hub chain, although he's sure it was working fine. I've just about managed to reconnect it, but I can only get it a couple of turns onto the screw thread, and the trigger won't pull down out of the top position. The hub chain itself is fairly stiff and bent against the links. Is there something I'm missing there?

For the lighting, I'll try changing the front bulb. I don't intend riding at night, so I'm not too bothered about how effective the lighting is (which is just as well by the sound of it!). If the tail lamp is not OE or period-correct, I'd quite like to swap it. I'd have to move it to the other side anyway for riding on the right here (the bike came from the UK). Anyone know of a nice-looking tail lamp to fit the rear fork? All the ones I've seen seem to attach to the rear mudguard, which I guess wouldn't look right.

Sorry for all the questions, thanks again guys