1. In 3-quart saucepan over high heat, heat potatoes and enough water to cover to boiling. Reduce heat to low; cover and simmer until potatoes are fork-tender, about 10 minutes. Drain.
2. Meanwhile, in 2-quart saucepan, hard-cook eggs. In 10-inch skillet over medium-low heat, melt 3 tablespoons butter or margarine; cook bread cubes, stirring frequently, until lightly browned. Remove skillet from heat; set aside. Drain oysters in sieve, reserving 1/2 cup liquid.
3. In same 3-quart saucepan over medium-low heat, melt 3 tablespoons butter or margarine; stir in flour, bouillon, salt, and pepper. Gradually stir in milk and oyster liquid; cook, stirring constantly, until sauce thickens and is smooth. Remove saucepan from heat; stir in parsley.
4. Preheat oven to 350°F. Grease a 2-quart casserole. Shell hard-cooked eggs and slice. In casserole, place one-third of the bread cubes, half the potato slices, a third of the sauce, the drained oysters, green beans, and egg slices, half of remaining sauce, rest of potato slices, remaining sauce, and remaining bread cubes. Bake 35 minutes, until bubbly.