Nev's Swedish Meat Balls in Sour Cream Sauce

Meatballs
1/2 lb. each: beef chunks, fresh port and veal (all fat removed)
2 Tbsp. bread crumbs
1/4 cup cream
4 Tbsp. finely diced beef marrow
2 Tbsp. butter
1/2 cup chopped onion
1 Tbsp. finely chopped shallots
1/2 tsp garlic
1 tsp. grated lemon rind
2 Tbsp. parsley
1 Tbsp. salt
1/2 tsp. black pepper
1/2 tsp. thyme
2 eggs
3 Tbsp. butter
2 Tbsp. vegetable oil

Sauce:
2 Tbsp. flour
1 cup brown beef stock
1/2 cup sour cream
2 Tbsp. fresh dill or 1 Tbsp dried dill
1/ tsp. lemon juice
salt
1/8 tsp. cayenne