Thanks Pat, at least I knew it was possible before embarking on the
nightmare.

How it went:
Airbox and intake off. Contortionists act to release the cap, forced the cap
and leads under the rigid water pipe, screwdriver to force the rotor off and
then found the cap also has a 'spacer ring'. D'oh. It was this that was
arcing in the first place. Down to Repco again and got leads and rotor as
well - both well stuffed but could have been cleaned up (90k). Not likely, I
don't wanna do this mongrel job for the next 100,000km. Anyway, slipped the
spacer and rotor in from the front and had fun and games getting it to seat.
Threaded leads down from top and fitted to cap. Where the coil lead goes
I'll never know - even a torch was useless!
The intermittent misfire is history.
Thanks,
Gaz