So, now testing the coil on the correct multimeter setting gives 4.1 ohms. Bought a new one before I realised and that read 3.8 ohms so I don't think the old coil is the issue. However, still no spark so I'm going to swap out the contactless ignition with the old points in case it's that that has died. To fully rule the coil out, can I put a spark plug directly in the HT lead coming from that, bypassing the distributor?
Thanks for the thoughts on fueling. I'm tentatively thinking that the smoke was due to incomplete combustion if it was that the spark was weak/dieing but of course can't rule it out. As I've said, was running great and went very suddenly which in the past, I've associated with ignition problems...