Inside the box are four mint NOS Folded Line triple-spring reverbs, assembled into two humbucking pairs, surrounded by appropriate impedance matching circuitry.
Mechanically, the reverb pairs float inside the box, surrounded by a layer of resilient foam padding.
Electrically, the inputs and outputs are completely isolated from each other. The inputs share a common chassis ground; the output grounds are isolated from the chassis ground and from each other. There is no possibility of ground loops.
Logically, this arrangement is like a reverb chamber; the outputs can be thought of as coming from a pair of microphones inside the box.