Joshua, Ive just flicked through my copy of, the life giving sword and can find no specific translation, of seigan, please except my appoogy.
However, on page 139, in the illustrated catallouge of the shinkage ryu martial arts the, en no tachi, "when your opponent takes the chudan stance, aiming the tip of his sword at your eye`s........" , this I believe is what is ment by taking the seigan stance, as in, seigan no kamae. As I understand it, some schools call this chudan, others seigan, when talking about this specifically. Again please correct me if I am wrong in this matter.
On another note, I understand its the owari line not oyama, that is now the main line yagyu shinkage ryu. I was at work when typing my last post and rushing the reply.