People have had mixed results with iridium plugs, but reliable results with NGK copper core plugs changed every 30000 miles. That said, I don’t think these plugs or coils are a problem for you because the misfire stayed in cylinder 2. Fingers crossed that the leak down and compression tests tell you what you need to know. If not from a head gasket issue, the misfires could be caused by something like a rocker arm being loose or falling off, which has been known to happen.
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