Beware of entering into an entertainment-based project with the term "educational" on your mind. I do not read fantasy, SF, or any other fiction with the primary intent of learning anything. I read to be entertained; if I learn something, that's a side effect. Few things will turn a reader off, whether they're 5 or 105, like an author attempting to educate them via fiction. There's a whole section of the library devoted to educating the reader - it's called Nonfiction. I picked up a Fiction book for a reason, dang it, and that reason was not because I was too lazy to parse the Dewey Decimal System to find a Nonfiction book!
Sorry. /rant
It's up to you whether to base your fantasy on existing 1950's or on alt-history 1950's. If you're feeling overwhelmed with the prospect of creating an internally consistent alternate world, then start with existing history and tweak only as needed. Basing that decision on perceived educational value is a mistake, not just for the reason mentioned above, but because, by writing a fantasy novel, you're already deviating from known history. Think that way, and you'll either feel guilty for deceiving your readers or straightjacket yourself into a textbook.
Write your story. Worry about whether I could pass the Twentieth Century History exam after reading it later.
JMHO...
