From the 1920s and 1930s:
"The Man Who Liked Ants," a short story by Leslie Charteris in which the Saint unmasks a plot to unleash evil high-IQ ants created by a mad scientist; if they aren't stopped they will replace humanity! This could easily be spun out into a full length film.
Men Like Gods by H.G. Wells. The first paratime novel, and wouldn't require expensive special effects. Wells' utopian speculations can be easily excised, leaving the people from our world who try to seize power in the other world but are foiled in a very amusing fashion. The accidental cross-time travelers would have to be changed from Brits to Americans and made into Chicago gangsters rather than London toffs. Edward G. Robinson would be a natural for the villain.
From the 1940s:
What Mad Universe (1949) by Fredric Brown. A complicated, highly intelligent satire that could be done with or without expensive special effects. Just imagine Leigh Brackett as the screenwriter...Ed Wood acting the role of the nerdish s-f fan...Ida Lupino as director...James Arness as the monster from Sirius trapped in a cage...Carey Grant as the hapless hero thrown into the wacky alternate U.S. that is at war with aliens...early Marilyn Monroe as Betty Hadley (three separate Hadleys, one being Grant's fiancee in Universe 1, the second being the financee of the nerd-turned-superhero in Universe 2 and the third being Grant's wife in Universe 3--all this is simpler than it sounds and would provide great opportunity for Monroe's comic talents). The scene with the Tappers could have become a sensation.
Grand Canyon (1942) by Vita Sackville-West. In an alternate World War Two, Nazi planes roam at will over an unprepared U.S. They bomb a hotel above the Grand Canyon while attacking a nearby airbase, and the guests retreat down to the bottom of the canyon. After several days they discover that they are all dead--victims of the bombing. This could be told on film in the manner of the popular Topper movies but with a patriotic twist--the ghosts determining to do their best to help defeat the Nazis. This last point is not in the book but would not conflict with Sackville-West's intent which was (at least in part) to strengthen U.S. support for the war. (Note: to make the plot viable for film one would have to add Nazi paratroopers landing at the hotel as part of a larger invasion force coming in from Mexico.)
I always enjoy Charteris Saint series. He would have fun every so often with a story that was Science Fiction or Fantasy base. But I was not planning to mess with the Saints Adaptions in the Timeline. A low budget studio might rip off the story in the 1950's post Them as the basis for a low budget sci fi story. I consider it.
I forgotten about Men like Gods. Will try to include it as a film but it will be in the 1950's. Good pick.
I like your Idea of What A mad Universe. But I have to lose Ed Wood involvement. How ever I love the idea of Marilyn Monroe in the film and Ida Lupinio did a great job directing the Hitchhiker. I never understood why she did not do more directing. So i planing for her to do some other thrillers in the 1950's and early 60's. The only one I got her lock down on at this time is A tv adaption of Fleming Moonraker.
And when I get to the 1960's ,Marilyn will get a Best Actress for Some Like it Hot. (My favorite film of hers.)
And Now I want to reread What a Mad Universe.
I do not know Grand Canyon. I will track down a copy. What thing I been enjoying doing this project, is people are mentioning some stories, I never heard of , so I checking them out.
Thank you for your suggestion.
If you have any suggestion for the 1950's , I started a page for that
https://www.alternatehistory.com/discussion/showthread.php?t=252930
and I also looking for Mystery and Thriller suggestion.
https://www.alternatehistory.com/discussion/showthread.php?t=252931
Thank you