story identification - Seeking book where disembodied brains run factories

I read this book in the late 60s or early 70s, but don't know how much earlier than that it may have been published. If anyone can identify the book and/or author, I will be most appreciative.

The story was set in a future in which all the needs of society are met by giant automated factories. These factories are controlled and operated by disembodied brains which have been removed from deceased individuals and "wiped" to erase vestiges of personality, or so it is believed. There is a young couple who work for the corporation that owns the factories and somehow they both get killed and their brains are put to work in the factories. They "awaken" and eventually realize with horror that all the brains running the factories are, in fact, still the people they once were, though in most cases driven insane by the knowledge of their situation.

Somehow, the two lovers avoid this fate and find a way to communicate with each other. They hatch a plan and find an out-of-the-way part of a factory in which to conduct experiments remotely. An early experiment results in an autonomous biotechnological "toad" they can control and one scene has the toad hopping around the factory floor, or outside, or somewhere. The experiments evolve in complexity until they are able to reproduce, more or less, their original human physical bodies, with adjustments that allow them to control the bodies remotely. They then use these bodies to sabotage the factories, release the imprisoned brains from their nightmares, and basically end "civilization" as it was then known. The book closes with them (their avatar bodies) sitting on a knoll in the rain watching the factories explode and burn in the distance, and then keeling over as the destruction consumes their own brains.