I recently was reminded of one of my all-time favorite unmade movies: KING KONG VS. FRANKENSTEIN. There isn't a whole lot of insight I can add to the page I just linked regarding the KING KONG VS. FRANKENSTEIN project, but I'll tell you how I learned about it. That's always fun, right?
I discovered plenty of interesting books lurking in my college library back when I was earning my degree. Two of them were were by Donald F. Glut: Classic Movie Monsters (1978) and The Frankenstein Catalog (1984). I studied both of those books thoroughly, and learned a LOT. Some of it proved inaccurate, but you have to start someplace to discover the true answers. Both are great books, even with the passage of time since their publication. Donald F. Glut definitely put me on the right path.
Anyway, I bring this up because it was in both books that I was exposed to KING KONG VS. FRANKENSTEIN. One fact that the page above perhaps selectively omits is that there was a middle title between KKVF and KING KONG VS. PROMETHEUS - KING KONG VS. THE GINKO. No, not exactly awe-inspiring. I believe the thought was that the monster's name was a derivation of Kong's name.
Well, as you probably know if you read the link, KING KONG VS. FRANKENSTEIN ultimately evolved into KING KONG VS. GODZILLA. But as much as I enjoy that film, I still find myself wondering, "What if?" regarding KING KONG VS. FRANKENSTEIN.