Re: Aiki Ken and Ken justu
Regarding the shared principles between taijutsu and bukiwaza (aikiken/aikijo). I train in Iwama-style aikido and more or less all movements in our taijutsu is in the bukiwaza-curriculum.
Some aspects of "aikido as I know it" (lots of stuff missing there) is easier to train with aikiken (hanmi, breathing, power generation, posture, maai, awase, keeping centerline). That said, Iwama aikiken is rather clumsy, I see it as "bukiwaza done as taijutsu" where as for ex Nishio-stylists feels like "taijutsu done as bukiwaza".