Place pork shoulder, pork loin, and pork neck bones in a large pot; cover with water. Add 1 head of garlic and salt to taste. Bring to a boil, reduce heat and simmer until meat is tender and cooked through, about 1 hour. Stir in hominy; bring to a boil and simmer for 20 minutes.

Place tomato and guajillo chiles in a pot and add enough water to cover; bring to a boil. Cook until chiles have softened, about 15 minutes; drain.

Place tomato and chiles with salt, 1 clove garlic, oregano, and cumin in a blender; add 2 cups of water. Blend until smooth. Strain mixture through a fine-mesh sieve and set chile sauce aside.

Transfer pork to a work surface and shred with 2 forks. Discard pork bones and garlic.

Stir chile sauce and shredded pork into the pot. Simmer pozole until flavors have blended, about 5 minutes.