Preheat the oven to 350 degrees F.
Place the salt, pepper, mustard, honey, 1/2 cup of orange juice and 1/4 - 1/2 cup olive oil in a blender or mixer of some type, and blend until thoroughly mixed.
Slice the oranges very thinly. Place the pork loins in a large casserole pan.
Pour the 1 1/2 cups of orange juice over the pork.
Drizzle some olive oil over the top of the meat.
Pour the orange juice dressing mix over the pork loins.
Place the orange slices on top of the loins.
Roast for about 3 1/2 - 4 hours until tender.
The meat will virtually fall off the bone when you slice it. It is so tender and delicious.
NOTE: If you are using a bigger piece of meat, you can easily double the dressing mix.