Bring a large pot of water to a boil for the pasta. Salt water and cook pasta to al dente.
While pasta cooks, toast rye bread in toaster then butter hot bread. Coarsely chop bread and place in food processor. Add parsley and paprika to bread and process into bread crumbs, reserve.
Heat a sauce pot over medium heat. Add butter to pot and melt, whisk in flour 1 minute then milk. Season the sauce with salt and pepper, thicken sauce 5 to 6 minutes then stir in mustard. Melt 2/3 of the combined cheeses into the sauce.
Drain pasta and return to hot pot. Toss hot pasta with chopped meat and sauerkraut to combine, stir in cheese sauce and coat. Transfer mac n cheese to casserole and top with bread crumbs and remaining cheese. Brown under broiler 3 to 4 minutes, serve.