Are you sure?
I only knew he practiced the kenjutsu of Inaba Sensei and did also the aiki ken of Iwama?
I may be mistaken but what I meant was he based his method on his studies of Kashima Shin Ryu (also the basis of Minoru Inaba Sensei's kenjutsu, I believe) and other sword techniques which he may have picked up from the Founder (Iwama aiki-ken?).
Shoji Nishio Sensei mentioned in one interview that he had planned to exchange ideas about weapons technques with Yamaguchi Sensei, but this did not push through.
Some mention of Yamaguchi Sensei's swordwork can be found here:
Kashima Shin Ryu has links to Aikido through Seigo Yamaguchi, whose swordwork was influenced by the school, and through Minoru Inaba, who teaches a limited portion of the curriculum along with Aikido. There are no (to my knowledge) direct links to Morihei Ueshiba's swordwork.
This is my understanding of the matter and I would be happy to be corrected / clarified.