Thank you Bruce and Steve for the input. As for other marks, the tsuka, saya, and other fittings were not military and I could not find any other marks on them. I found one reference that suggested the Dai (or O, or Tai, or Y as in Yamato) was used at the Tokyo Arsenal 2nd factory in Kokura at least on the Nambu pistol. Additionally, I found another reference that listed the second mark as a principal inspection mark at the same factory (that may have been from a page posted by you, Bruce). Here are some further pictures of the sword, which may help in identifying it. Its overall length is 57.5cm with a 44.1cm cutting edge. The registration card indicated it was registered in Okayama Prefecture in 1965. And thank you all again for the assistance.