There is a passage in the final part of "The Second Interment" which reads:

"He thought that he was lying captive in some Inquisitorial vault whose roof, floor and walls were closing upon him with appalling speed, were crushing him in their adamantine embrace."

I wonder if Smith thought of "The Pit And The Pendulum" by Poe or "The Iron Shroud" by William Mudford. My money´s on Mudford. :-)

I'd say Arthur Machen's "The Novel of the Iron Maid," maybe.

"A Terrible Strange Bed" (1852) by Wilkie Collins also deals with a hellish and insidious mechanism crushing the victim.