Hops are so unimportant in a stout you could use almost anything. If you have access to willamette or any other fuggles varieties that is great. Challenger would be great for bittering as well as northdown, brewers gold, etc., etc., etc,.. It's great to see people finally learn that so many hop varieties are so similar and adapt to what they have...without even being able to tell the difference usually.
You could use any of the high alpha hops for your bittering without much impact on the flavor. With a high alpha hop you don't use much hops at the bittering stage so the contribution to flavor is minimal. In stouts the roast flavors are strong enough to mask the minimal hops flavor. In paler beers or in late additions then you have to be more concerned.