For the pork: Sprinkle the pork with the salt and pepper. Heat the oil over medium-high heat in a 5-quart saucepan. Cook the pork until brown, about 10 minutes. Add 3 cups water, the chicken broth, orange juice, cumin, chiles, garlic and onion. Bring the mixture to a boil. Reduce the heat to a simmer and cook until the pork is very tender, for 2 hours. Shred the pork into small pieces, using 2 forks. Season with salt and pepper.

For the salsa: Cut the ends off the oranges and grapefruits, place cut-side down on the counter, and cut away the peel. Using a paring knife, cut along the membrane on both sides of each segment. Coarsely chop the fruit segments. Squeeze the juice from the membranes and reserve. Whisk together 2 tablespoons of the reserved citrus juice, oil, honey, vinegar, salt and pepper in a small bowl until smooth. Add the fruit segments and toss until coated.

To serve: Warm the tortillas by holding them over a burner for 30 seconds on each side or place in a dry skillet and heat over medium heat until warmed through. Place 1/4 cup of shredded cabbage in the center of each tortilla and place the pork on top. Spoon the salsa over the meat and serve.