You are unlikely to find information that is going to fulfill your criteria of "legit" information on this topic.

From what I can tell, all this Merkaba information comes from Drunvalo Melchizedek who was supposedly given the memories of Thoth going back through Egypt to Atlantis where he was a king. There is no solid supporting evidence for any of this story, but it's an intriguing one nonetheless. At the very minimum its some pretty heady sci-fi. At best it's still  the source of all this information on sacred geometry which is something I know is of interest to much of the membership here.

If you've ever seen the Spirit Science videos on youtube, particularly the one on human history and the sacred geometry stuff. It's a nice cursory overview of Drunvalo's story. If you are interested in digging into it a little deeper, Bob Frissell's books (Nothing in This Book is True, Something in This Book is True, You are a Spiritual Being Having a Human Experience) really delve deeply into this information. You can also just go straight to the source and reead Drunvalo's books.

A lot of the information stresses credulity but some of it is really quite interesting, I really dig the sacred geometry stuff and feel there is some validity to that, even if I don't necessarily buy the stories of Merkabas on Mars and the kingdoms Atlantis and Lemuria.

I'd suggest if you choose to delve into what's behind all this Merkaba mumbo jumbo, that you check your credulity, skepticism, and stipulations that information must be legit and cited at the door and enjoy the story for what it is. Just like going to the movie theater, enjoy the show first, then re-engage your skepticism and tear it apart for a critical scathing review afterwards.