I haven't torqued my header since i installed it 2 years ago, and there's no sign of needing to. I did however use high temp thread locker on the studs and nuts..
If you go with remflex, there's no gasket sealer needed. These gaskets simply mold themselves into all the crevices on the head and header.
I like your idea of a lock washer, nut and jam nut. If i ever have to replace these, I'll probably go that route.
About not torquing the header since install: I've checked it with a torque wrench about a week after, then a month.. but every time, no spinning, just clicking.
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