My birthday present arrived a week early, so I've been reading Stephen King's addition to his Dark Tower series, The Wind Through the Keyhole the past few evenings. The DT series is one of my favs, and really the only stuff by King I've read in the past decade has been those books and a few related works.
And since I'd always wanted to run a game set in the DT universe, my mental gears have been churning away at ideas.
Many years ago, I thought of using d20Modern/Future/Past/Apocalypse to make it work.
Now, I think Labyrinth Lord as the base set, Go Fer Yer Gun for PC classes, and Mutant Future for additional monsters and artifacts. It could work.