Hi - Thought I'd let you all know that I managed to fix the problem without changing the source coil
I removed the flywheel and the stator plate took all the coils off and cleaned everything thoroughly including the wiring harness connectors.
Put it all back together and she started first kick
Note that the source coil resistance is still only 180 ohms instead of 240ohms so if you experience a similar reading it doesn't necessarily mean that the coil needs replacing
Restore nearing completion now - will post some photos in due course