I asked Inaba sensei a bit about this earlier today (lucky me!).
He said that Noguchi sensei was a fellow student of Yamaguchi sensei and also was more present in YS's dojo - meaning he was there for more years and also spent some of that time teaching or at least regularly substituting on YS's behalf. Noguchi sensei studied with Kunii sensei for a little less than Inaba sensei, but also had the direct transmission.
Inaba sensei continued to study aikido with Yamaguchi sensei, and teaches it alongside the Kashima no Tachi as in his view the need for relaxation alongside the sharpness and focus of the sword is totally necessary.
Sekiya sensei took the decision at the age of 70 to study with Inaba sensei at the Shiseikan - quite a statement of recognition given his age and experience. Was discussing earlier with Paul Smith and SS apparently said his body got better after 70 from that study. I think that SS influenced IS to "open up" to westerners more - for which people such as myself are a direct beneficiary and very grateful!
When I asked Gleason Sensei about this he told me that Noguchi Sensei would teach sword informally before Yamaguchi Sensei would begin to teach
Gleason Sensei also told me that Inaba Sensei would train there sometimes as well, but trained separately from Noguchi Sensei
These's some super 8 footage of Noguchi Sensei performing the Kihon Dachi and Ura Dachi katas included on Gleason Sensei's dvd On it you can see the strength and sharpness of Noguchi Sensei's technique