I picked up a book called "Killer Kaiju Monsters." It is a very....interesting (maybe not the best word) perspective on Japanese films. The author isn't anyone I recognize in the overall fandom, but he is described as a "long time resident of Tokyo" -- which explains his indirect "expertise" in kaiju movies.
About half the book is about Godzilla/Gamera films with the other half dedicated to artwork of Japanese artists, including the one who did the extensive "cut-away" views of many famous film monsters, showing their organs, bone structure, etc.
Not everything is accurate, but it made me realize that I don't think any book is "accurate" because authors of such books were never on the studio floor making the films. For example, he describes Gamera as "the hero to young boys." Wasn't it "hero to all children?"
He also tells how in "Godzilla Raids Again" that it was Angilas' high-pitched roar that cracked and shattered the castle in Osaka during the final battle with Godzilla. I thought it cracked because of the overall battle going on..?
He also interchanges film titles...listing films as "All Monsters Attack" and "Invasion of Astro Monster" as the "English" (UK?) titles for "Godzilla's Revenge" and "Monster Zero" along side "Destroy All Monsters."
Anyways, I bought it for $1.99 online. There's also a section on vinyl kaiju and "Kaiju vs Yokai." It was a fun read, but a very different view on the genre, as if by osmosis.