I have seen your electrical gremlins before. Do yourself a favor if you have not and run a good large ground cable between the battery and the cylinder head. You would think the headstuds etc would be enough of a ground, but I saw a spitfire go through a similar scenario and grounding the cylinder head solved it. We also fixed a VW IT car that had a high rpm miss by grounding the cylinder head. I read this in Circle track years ago. On V8's they ground both cylinder heads. The ignition system depends on good grounds. Electricity seeks the easiest path to ground. Insure it has that path. It won't hurt and if anything it may help.