..."How the hell do you hide the launch of a 365 foot tall, 7.6 million pound thrust booster?"...

You don't. Even if launched from the middle of the Pacific Ocean, which was absolutely impossible without the required and unconcealable launch facility, foreign nations (especially Russia) would have noticed through various measures, including satellite and radar observations.

Consequently, there was no Apollo 20 mission, and you are correct: the story is self-evidently bogus.