[kiwi nz]

You have done everything except swap the distributor, at least I think so. Too many pages to go back and check, but it seems to me the whole ignition system needs work.
Starting with the distributor.
It is a long time since I have had a problem this vexing, but when I have had it has always been " the assumption, the overlooked or the misunderstood".
Guilty of them all your Honour.