Big Change-Update: Using a professional fabrication shop, the box is now welded, with a gasketed door, and mounted with stainless steel 2-bolt clamp on top. Also a little larger than original box. Sells for $199 plus $15 shipping in USA. Check out current boxes at www.advgear.net-
You'll have to drill a small hole in the two lower pannier mount tabs, other mounts just bolt in.
It is necessary to remove the crud catcher, it'll hit the box when the suspension compresses.
Photos further in this post may show the older, riveted version. The new welded one is cleaner, lighter and bigger.
More photos on the advgear.net site