Scrub the clams well and rinse under cool running water. Place in a large pot with the beer and water and cook, covered, over high heat, until clams open, 5 to 6 minutes. Remove the clams from the shells and discard shells. Strain broth and reserve separately. Add enough hot water to the broth to make 4 cups.
In a saucepan, cook the bacon and chorizo until crispy, remove from pan and reserve for later. Add the onion, celery and green onion to the bacon fat and saute until transparent, 6 to 7 minutes. Add the flour and the butter, stirring until well blended, until fragrant but not browned, about 3 minutes. In a separate saucepan, bring the milk and the cream to a simmer and keep warm. Gradually add the broth to the vegetable-roux mixture and bring to a boil. Once the broth thickens slightly, add the potatoes, corn, salt, pepper, nutmeg, and paprika, and cook at a low simmer until potatoes are nearly tender, 12 to 15 minutes. Add the clams, hot milk-cream mixture, and cook until mixture is heated through, about 5 minutes longer.
Garnish the stew with the chopped parsley and diced red pepper.