The boat has always been in my parents garage and seems big but may not be 20’ long. Looking online a bit more it seems like the plans are for the dingy. Zephyr article.
As far as building it – my dad bought the plans back in the late 50s or early 60s. He and 6 engineering buddies built 5 of the boats from the plans. They had a great time doing it. My dad’s never got completely finished but others were in the water and sailing. He died last year so I can’t add any details. That’s why the boat is now available to a good home. If you know anyone who would be interested, or a place where we should advertise it, please let me know.