It's all about the yeast. WLP570 is the Duvel strain, so that's the way to go. Otherwise, keep it simple. 1.070ish, 80% Pilsner Malt Extract, 20% simple sugar, and about 30 IBU's of Saaz at the start of the boil. Pitch in the mid 60's and let it work its way up to the mid 70's.