Those with a particular interest in the Reikai Monogatari might be interested in this website:
http://www2.plala.or.jp/wani-san/briefsummary.html
On the following page, the website includes a very detailed account of Deguchi’s Mongolian adventure:
http://www2.plala.or.jp/wani-san/briefsummary5.html
The information on the website, including the Mongolian account, looks (to me) to be well-researched, but I don’t see any identification of the website’s author.
Dan