I used grade 8's on my 218 with ally head and nearly cost myself dearly, threads all properly cleaned, thread seal applied then torqued in sequence. Re torqued after first heat cycle and all seemed well. Truck was idling when I heard a strange metal bang noise, engine was still running but I could not see anything odd until later that day I was admiring my handy work and noticed one bolt head didn't look as tight down as all the rest. Turns out it had snapped inside the head level with the top of the block.
All bolts were immediately replaced with ARP studs and nuts which can be torqued down more as well, not cheap but cheaper than a new Edgy head, since then no problems head wise, plenty elsewhere but head good!