I'm sure you've seen http://issuu.com/dulcimerplayersnewsinc/docs/25.04.1999watermarked
which is also reproduced here in a more easy-to-read format http://www.richardandmimi.com/hennessy.html
That's all I know of that's been written about it. The instrument is in the Smithsonian Institution where it is put away so that none can see it because of "space considerations." I want none of my instruments to be put there when I'm either gone or incompetent. The only instruments which should be given to them are ones that cannot be repaired enough to be playable.