In the junior novel Indiana Jones and the Mystery of Mount Sinai, the author reuses these scrapped ideas for the main villain, whose name is Mephisto (which I believe was Toht's original name), a Nazi with an electrically-charged mechanical arm.
I liked the book as a kid, because it was a new Indy adventure taking place in the 1940s that was released at the time of Skull. However, after rereading it as an adult, it kinda sucks. It's a direct sequel to Indiana Jones and the Pyramid of the Sorcerer, which, while also not great, was enjoyable enough. Sinai completely changed the personality of the female lead from Sorcerer, for one, which was very annoying to read. The story itself also just wasn't very engaging.
And if you didn't like the aliens in Skull, you won't like the extraterrestrial origins of the MacGuffin in Sinai.
From what I remember, anyways...