Thank you all for your assistance! I have contacted Robert Benson, and he has agreed to clean the sword enough to examine it. I will be sending the sword to him this week. I'll keep you updated.
Mr Benson did mention that "the Sayagaki is by Inami Hakusui is not reliable", saying that over the years since 1964 he has never seen one of their appraisals that was accurate. Is that the general consensus around here?