Well...assuming that nothing else has changed on the car, it either has to be a bad ground or some serious resistance in your ignition system somewhere. The reason wires will arc like that is because electricity always follows the path of least resistance. Usually that's to the plug but if for some reason the plug is bad or the ignition system is unstable then the electricity will find an easier path whether it be to another wire, a header, or the head. If it's doing it on ALL the wires, it's almost certainly a ground problem. If it were one or two wires I'd suggest you change plugs again. Double and triple check every ground in your ignition and electrical system (a pain, I know, but that's gotta be it). Check the MSD ground and the coil ground first. Good luck.
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1984 1/2 GT350 (#842 Hatchback w/ T-tops), 302HO, Comp cams Xtreme Energy cam, Carter 625cfm carb, Weiand Stealth intake, MSD distributor, MSD coil, FMS 9mm wires, 1 5/8" MAC unequal shorties, 2 1/2" MAC Prochamber H-pipe, Flowmaster 2 chambers, KYBs, 16"x8" 4 lug Cobra Rs, Falken 245/45ZR16s
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