Pickup in the distributor failing hot.

Obviously you have a problem that crops up when the component is hot, bench testing cold does no good. Did you actually put a new distributor in the engine or did you "then hook aup another distributor , earth it. spin shaft by hand , it has a beautiful full spark!." That tells you nothing.

Ballast resistor is bypassed when starting.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.