Robert S. Conley, this supplement brings the Wilderlands to the Swords and Wizardry system. As Moritz mentions in his blog, it should be easy to convert to any pre-D20 D&D edition. Blackmoor first saw print as Supplement II for OD&D. Having The Majestic Wilderlands be marked as Supplement VI makes for a nice connection between the two worlds. The connection between Blackmoor and the Wilderlands goes back to the First Fantasy Campaign in which Blackmoor was linked with Judges Guild's house setting through the Valley of the Ancients.
Edit: Conley has started a discussion of this product here.