Dear Charles,
I once had the chance to examine an Emura blade and, like you, found it to be a thoroughly practical, combat-ready piece.
Mr. Omura’s article contains an obvious contradiction: on the one hand he describes a large-scale, mechanised shop, while on the other he insists that Emura-san personally performed every yaki-ire. If the machine totals and manpower figures are accurate, the warden would have had no time left for prison administration—he would have spent every minute quenching blades (•_•). My guess is that he must have trained a small group of inmates to handle at least part of the heat-treatment; the report is probably not as literal as it sounds. (I don’t doubt the existence of the hammers—East-Asian penal institutions have long used similar labour schemes, and a state-sponsored workshop could certainly obtain both machines and men far more easily than it could obtain one warden doing every single quench.)
All of the above is only my own speculation and rambling, of course; I hope it doesn’t spoil your mood. Like you, I’m still hoping for hard figures and solid documentation.
Best regards,
Sam