I'm putting a new plug cap on, and the HT lead is looking a bit scabby (and has a suppressor) on what looks like an original coil - can I swap just the lead?  Or do I just fit a new generic coil?

I know you can splice on a new lead because that's what I did with my 348. I didn't try and take the old lead out of the coil though. I spliced at about 25mm from the coil casing.

There's nothing wrong with fitting a new aftermarket coil either, but getting one that fits in the available space might be tricky.