I found this Japanese Science Fiction magazine from around 2002 that had a page about what seems to be an anatomy of Gamera and Legion
Gamera: https://pbs.twimg.com/media/E88soPHWQAEs5Uc?format=jpg&name=large
Legion: https://pbs.twimg.com/media/E88srsWXoAU8LdA?format=jpg&name=large