Tough beer to clone using Extract... I would recommend at least bumping up to Partial Mash. The problem with using Dark LME is that it usually contains a decent, usually undisclosed, amount of crystal, munich, black, amber, and/or chocolate malts already in the dark extract. So if you top on more specialty grains, you might overdo it. I would advise starting with an extra light base of DME and build from there with other mashing and specialty grains. A Partial Mash recipe will also help a little more with more attenuation/fermentability if the proper steps are followed.
Some facts and rumors:
Ranged anywhere from 10 - 11% abv over the years. Search here for a compatible yeast strain: http://www.wyeastlab.com/hb_yeaststrain.cfm
Small amount of debittered black malt?
8 oz. Cocoa powder + unknown amount of Bittersweet Belgian chocolate (added at end of boil)
8 oz. Chocolate extract (added when bottling)
Cocoa nibs in secondary
Kettle hops: chinook & willamette (I imagine a very simple 90/30 schedule or something similar)
3 months bottle conditioning