Hello!
I am also interested in ki61 due to its license-built DB601Aa.
Do you have a japanese edition Famous Aircraft of the World No.17 1989-7?
Difficult to read japanese but many strong info.
It can be downloaded as 18,7 M pdf file from there:
http://www.zshare.net/download/61kibu-rar.html
Downloaded file can be opened using password PF42.
As for me file opened succesfully.
All the best.
Igor.