Hi Lan,
Just about every publisher had his own horror title. Often more than one.
I'd suggest just checking under each publisher and looking for any obvious sounding names.
ie
Ace - Baffling Mysteries, Beyond, Hand of Fate, Web of Mystery
Ajax-Farrell - Strange Fantasy, Voodoo
Avon Comics - Eerie, Witchcraft
American Comics Group/ACG - Adventures into the Unknown (predates EC as first horror comic), The Clutching Hand, Out of the Night, Skeleton Hand
Better/Nedor - Adventures into Darkness, Unseen
I'm sure you'll find many many more on your own.
But NOTE - some precode horror comics got especially gory over time as the field became glutted with more and more books all competing for the same dime. Even EC would falter and publish a few stories that crossed the line late in their history. So I'd strongly suggest checking each story you consider closely before using them.
Good luck with the project.