You shouldn't have a problem. The Dura Ace headset is listed with a stack heights of 37.6mm, vs the Chris King #2 nut with a height of 37.4mm.
If the seller is honest you're in great shape.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.