For the dashi: Combine the kombu with 6 cups cold water in a medium pot and slowly bring to a simmer over medium heat, about 10 minutes; do not boil or the kombu will turn bitter. Just as the water reaches a simmer, remove and discard the kombu and add the bonito flakes. Heat to just shy of a boil, remove from the heat and set aside to steep for a few minutes. Strain into a bowl and discard the bonito flakes.
For the ramen broth: Wipe out the pot, add the oil and set over medium-high heat. Add the reserved shrimp shells and scallion whites. Cook, stirring, until the shells are brown all over, 4 to 5 minutes; the shells should make a crackling sound as they toast and brown. Add the dashi and shiitakes and bring to a simmer. Cook for 30 minutes, then strain the broth, reserving the shiitakes. Return the broth to the pot, stir in the mirin and seafood seasoning and set over low heat until ready to serve. You should have about 3 cups of broth. Stem and slice the shitakes and set aside.
Bring a large pot of water to a boil over high heat and cook the ramen noodles according to package instructions. Drain and rinse the noodles with cold water to remove surface starch and stop the cooking. Leave to drain.
Cook the bacon in a large skillet over medium heat until crisp, about 5 minutes, then transfer to a paper towel-lined plate. Pour half of the bacon fat from the pan into a small container to save for frying the noodles. Raise the heat to medium-high, add the shrimp and corn to the remaining bacon fat in the skillet and sprinkle with salt and pepper. Saute until the shrimp are cooked through, about 4 minutes. Remove the shrimp and corn to a plate, then add the reserved bacon fat to the skillet. Let the skillet get good and hot before adding the ramen noodles. Cook, stirring minimally, until the noodles are crispy and charred in places, about 3 minutes.
Divide the noodles among four bowls. Top with shrimp, corn, bacon, sliced shiitakes, scallion greens and shredded nori. Ladle ramen broth into the bowls and serve.