I did the lead swap, but it's not doing it at all now, so maybe a curve ball in my long term diagnostics. The next job is to clock the rockers and see if the cam is playing up on number one, eg, sticky valve or worn cam. Maybe it only does it...

One update I've noticed. Recently, when cold, it misses on number one cylinder for some time until it warms up. Still running rough, but even worse on 3 cylinders. I've pulled the plug and I'm getting power down the lead...I can still feel it...

Definitely does not raise the refs when I spray (sparingly) around the carb or intake areas. I think I can rule out air leak.