Sensei began by explaining that the Shinken Gata followed the same kata sequence as the Kukishinden Ryu with the exception of added kata at each level. The distinguishing differences between the Kukishinden Ryū Dakentaijutsu and the Tora no Maki is that the Dakentaijutsu takes into consideration that each movement is being done while wearing load bearing equipment such as yoroi.
This is not the case with the Shinken Gata. The techniques are done from a higher stance, where one does not need to be so deep and the taijtusu characteristic being changed to suit the movement and balance necessary when wearing Yoroi. They are characteristically fast movements.
My observation is that the kakehiki of the kata from Tora no Maki are no different from those found in the Dakentaijutsu, while the patterns of muscle memory within the taijutsu kata are different (at least up to Nidan.)
The timing and maneuvering of your opponent share identical details. Ie. Sei-on, very different technique, same kakehiki. (This could be my mistake and assumption though-this was not discussed with Sensei)
Regarding the history of Shinken Gata Taijutsu. Sensei explained that the Shinken Gata is not related to Kukishinden Ryū, for the exception of the names and sequence of techniques. It was created during late Edo Period by a man named Ichi Yanagi Kazuma, but Sensei has only been able to find one reference to this man’s name, it being found in the densho he copied by Hatsumi Sensei’s request. It is only written there.
These were Sensei’s words. I have since researched Kazuma and have discovered quite a bit more regarding his history.
Sensei also explained that the Shinken Gata included Bikenjutsu, Yari and Tenmon Chimon. He only had the Tora no Maki (Taijutsu) Sensei said that some people say that each part of Shinken Gata has a different name, and some say it is all Shinken Gata. He drew a diagram of this.