The rebirth ending triggers if you collect the obsidian goblet, white chrism and read the book of lost memories and book of the crimson ceremony. To avoid that ending just skip collecting those items.
Good luck with your project! I have tried to make the first game a few times, in a prototype version of game boy born from a wish if you beat the game and started another there was a door in heavens night that opened to a warp room with an air screamer hanging out over a door leading to silent hill 1 prototype...


how's this?