605s are copper, as well as stock 606s. Heat range has nothing to do with the material of the center electrode, although a platinum/iridium tip does hold more heat. It has to do with heat retained based on insulator length. Platinum Autolites have an AP prefix, double platinum are APP.
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'13 Mustang 3.7V6 - MT82
'00 GP SE (L67 Swap, XP, Headers, 3.25")
'98 GTP, '01 Bonne
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