I imagine 8 is a no brainer, invis in, single pull, slow, and melee/dot chief down. Any complications here? e.g. fight takes too long, etc.
I've done it with my 65 bard, and it was mostly straightforward.
Do the turn in, invis, and run into the camp. When the chief spawns, pull him around to the back of the fort (away from help) and lay into him both chants and melee.
At the time, the mysterious "mob warps away when he death marches" bug was in full swing. The chief did indeed warp and eventually die to my dots. I'd heard the warp spot was out to sea south of the big bridge, so I ran over there and used corpse locate with no target to find the nearest corpse. I got lucky and found him that way.
Then run back to the leader and turn in the head before he even gets his army moving. No problem. One catch: this is the part where someone else who has the head but failed the quest can sneak in and steal your quest. Best to do this when no one else is in the zone, if you are the paranoid sort.