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The frequencey shifter (also known as Klangumwandler) was first developed by Ludwig Heck and Fred Bürck for the studio at Südesetfunk, Baden-Baden. The most well known verisons of the device were made by Harold Bode, who moved to the US (worked for Wurlitzer) after developing some of the first electronic instruments for the Cologne studio. Among several of Bode's own models, there was also a version that was licensed to Moog and fit the standard Moog modular cabinet. This AES paper by Bode should answer most of your questions: "Solid State Audio Frequency Spectrum Shiter," AES Preprint No. 395, 1965.
Here's a picture of an early frequency shifter made by Bode (transformer in-out, hand wired, hand-labled frequency indicator!) for the then-Columbia-Princeton Electronic Music Center (now Columbia Computer Music Center).
Best,
James
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