Make the Broth: In a large stockpot, combine the chicken, ribs, leek, ginger, garlic, water and shoyu. Bring to a boil.
Meanwhile, in a skillet, heat the oil. Season the pork butt with salt and brown it well on all sides over high heat, 12 minutes; transfer to the stockpot. Simmer the broth over moderately low heat for 2 hours, until the pork butt and ribs are just tender; skim any scum that rises to the surface. Transfer the pork butt and ribs to a platter and refrigerate. Strain the broth and discard the remaining solids.
Return the broth to the pot. Add the kombu and simmer over moderately low heat for 1 hour and 30 minutes. Let cool, then chill and refrigerate the broth overnight.
The Next Day, Prepare the Ramen: Preheat the broiler. Skim the fat off of the broth and discard the kombu. Bring the broth to a simmer. Season with shoyu and keep hot.
Untie the pork butt and slice it across the grain 1/3 inch thick. Cut the ribs between the bones. Arrange the pork slices and ribs on a large baking sheet and brush with shoyu. Broil 8 inches from the heat for 3 minutes, turning once, until the meat is crisp; keep warm.
Divide the cooked noodles among 8 bowls and ladle 1 1/2 cups of broth into each one. Add the spinach in piles. Drain the eggs, cut each one in half lengthwise and set a half in each bowl. Arrange 2 slices of pork butt and 1 rib in each bowl and garnish with the scallions and nori. Serve the ramen immediately, passing the rice vinegar and togarashi at the table.