Just noticed this three page pdf document was added to his website on April 7th. An interesting read, imo.
http://www.hi-ho.ne.jp/amago/b-streams/flytying/pdf/Traditional_Kebari_Hook-E.pdf
It is linked to within the text of this document.
http://www.hi-ho.ne.jp/amago/b-streams/flytying/kebari_study.html
D