Hi Stig,
The book is Imperial Japanese Army Flying Schools 1912-1945 published by Schiffer.
There seem to be a few sites that give 3710, but without knowing what the source for the figure is, its difficult to reach any judgement on the accuracy. At the moment we have two sources, the above and Baeza, both of which one could reasonably view as credible. So the true figure is? Well, alas difficult to say.
Meanwhile here's a small vid of Ki-79s of the Akeno Flying School I believe. Perhaps best enjoyed with the music off:
http://hiroseorth.blogspot.com/2013/...g-post_22.html
Regards,
Clint