So Irwin Allen was a Film/TV producer who was putting out some spectacular work on a budget. Such a tight budget in fact that scenes from 'The Lost World' were used in the TV 'Voyage to the Bottom of the Sea' and Captain Crane had to get out of uniform to wear his old outfit from the earlier film.
Pity the ships of 'Lost in Space,' the ever popular Jupiter 2 and the lesser known Gemini 12. Not much resembling one another, they both appeared in the series as the Gemini 12 footage from the pilot was recycled for planet fall/crash sequences, etc. According to this the fullsize sets didn't match either one. I think their mockup for the SciFi airshow looks more like the Gemini 12 for the lack of room for a lower deck. But with the show over, Irwin Allen ordered them butchered for parts for the sets of 'City Beneath the Sea.' In the 1980's the Gemini 12 had a bad restoration and was put up at an auction. One thing Allen lacked a vision for was the memorabilia market, think of what he could have made off the two models if he'd protected them and saved them until the demand was there.
Dang, I wish this place with fullsize mockups really existed, even if they're not real spaceships it would be great for SciFi nuts like me to go inside.