I saw this system marketed as an aftermarket conversion kit. The system marketed under the Cyclo brand consisted of a Benelux plunger spring type 3 speed derailleur, a 3 speed cogset (fixed, I believe) that mounted to Sturmey Archer Hub, which did the freewheeling, and a derailleur control lever.
Now gone, Big Wheel Mail Order in Minnesota, sold these kits.
Paramounts could be built to customer specification. As such, it's not out of the realm of possibilities as being on a "made to order" Paramount.
The system is pretty uncommon. At the same time its doesn't have much mojo either.
I saw one (3 by 3 gear system) recently on a garden variety (mild steel framed) Flandria. That Flandria was from 1972 or so. It suggested either the system was lightly used or the system is relatively durable. I've never used the system personally.
Plunger type derailleurs were de riguer in the 1950's. It was mainstay for Simplex and Hurets. But the paralleogram derailleur proved far superior. It seemed quaint that this plunger type derailleur design was still being offered in the 1970's.
Todd Teachout
Hercules, CA