I managed to make a little more progress...
I fitted everything again that I thought I was going to have to remove to get the head off.
I had to re-wire the plug for the electronic ignition, as it fell apart when I disconnected it

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When that was done, I started it. But the tapping noise (which I thought was just from the spark-plug tip when it was in there) could still be heard.
So we now think it's an incorrectly adjusted tappet, probably put out of place by the s/plug tip.
I took off one of the cam covers to have a look-see, but didn't have time to adjust it.
Next available chance will probably be the next Uni holidays (around 8 weeks away)

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But at least the engine bay is looking good with the red and black theme

(Sorry, no pics

)