In 2014 I spent 2 hours at Mr Culbreth's residence with Soke Yamamoto to discuss Yoshukai Iai with him.
Soke showed me some bunkai for some of the waza and we also discussed the origin of Yoshukai Iai. Soke did not learn Iai from Dr Chitose but from 2 different masters from Kyushu.
Although I was not always able to fully understand what he was trying to tell me, I understood he had been training in the 2 styles of Tenshin Ryu and Jigen Ryu, and that when one of the masters he was training with died, he quit training in that style.
In this Tenshin Ryu video, you can see where some of the Yoshukai Iai moves come from.
Although Tenshin Ryu Nodachi is much longer than the regular katana used in Yoshukai iai, the waza at 1:40 is very close to the Yoshukai Waza #8, and the next one at 2:00 is very similar to our #7.
Also, Chiburi and Noto are the same.
Fred Lecut, Dothan Dojo