It's a great fairy tale.
Danvers was erected in 1878. He found these over 30 years ago,so lets say 1977 at the latest. Hmmmm... my math says 99 years at best, his says 110?
In 1977 Danvers was a working state hospital. The tunnels were used for utility maintenance and storage and access to them was restricted. What exactly was he doing in them and why would he assume he could take anything he found there home with him? (I was always told that's called STEALING.)
Humane restraints began making leather restraints for use primarily by state facilities like Danvers in 1876. It would seem more likely that an institution that was well known for progressive and humane patient treatment would be using them rather than towers products. Maybe these were used for the patients that kept chewing through the leathers?
And I e-mailed him and pointed out that I've personally bought towers bottom key handcuffs on e-bay. I even sent him the URL for a recent auction list from this forum showing a pair was sold in January of this year. His response was that he and 3 other collectors had researched it and there's never been a pair of towers bottom key cuffs sold on e-bay and I never bought any there. And don't bother to bid on them because he wouldn't sell them to me. Can't argue with logic like that I guess.