HELP!! need experts advice on 440 trouble.

....crack in headder that opens up when hot........I dont know, just throwin stuff out there,,,,heat crossover passage to ntake/ not sure if you have those....bad threads on one plug or the little spark plug washer/(gasket) (you might not have the either) maybe an arcing plug wire (probably not) misaligned hedder opening/gasket opening to head.
(prolly not though).........cylinder PSI is just fine IMO.