Obligatory preface: I’m not a lawyer! This is as best I know based on a bunch of Googling. Take it all with a grain of salt. That being said, we certainly hope you’re free to use it because we’re essentially sampling the whole thing. It’s not clearly in the public domain that I know of, but it is largely treated as an Orphaned Work since it’s all over the internet and no one has stepped up claim ownership. You’re probably fine to use it.

Well done! We are grateful for this thorough demonstration of your monsterological skills!