I may just be lucky (if true, it's a first) but an old trick was to tighten them down cold then run them through a couple heat cycles re-tighten each time.
Just get some stage 8 bolts and be done with it.it
it also depends on the header gaskets being unused. Some relax after a few cycles and some dont. When torqued, the stretch of the bolt should be enough to keep it from backing out, unless the gasket relaxes.
not like Ford sold you the car abs said “come back in 1k miles so we can retorque your header and intake bolts.