An English translation of part of "Takemusu Aiki" appeared in the last four print issues of "Aikido Journal", but has been discontinued. There are extensive footnotes, but even then, you can make sense of what O Sensei said only by reference to works like the "Kojiki" and "Nihon Shoki".
I have also discovered that the Founder appears not to have read the "Kojiki" directly: he acquainted himself with Japan's early myths through the works of Onisaburo Deguchi. There is a print version available of "Reikai Monogatari", but I myself have the electronic version. None of all this is in English, by the way, except for Philippi's translation of the "Kojiki" and W G Aston's version of the "Nihon Shoki".
Happy New Year.