my big problem with new extractors was blowing gaskets, after the third one, extractors came off and had my mate reface them, ported them also, these were 4mm out from the jig they used. My new gasket is a TC Cortina one, was at Autobahn and had much more meat around the centre ports, i still had issues refitting and bolts etc, bloody nightmare to be honest, tried studding a couple to at least locate the gasket, stud nuts to big and interfered with the pipe bends, i would like to see a set of extractors that would allow the use of a stud kit, then get a gear wrench to use to get them done up. At least get them faced up, this will help, i bet they are out, as far as heat goes, the head can take a lot more heat than the extractors. So it wont be the head. After watching a special on Pacemaker on Grand Tourer Dreams, i would buy these as my next set, my set are Hi-tech’s.