Drain mushrooms; reserve liquid.
Fry bacon with mushrooms until bacon is crisp; do not drain.
Add sugar, flour, salt and pepper to mushroom mixture; stir to blend.
Gradually stir in vinegar and mushroom liquid.
Cook, stirring constantly, until thickened; keep hot.
Cook macaroni according to package directions; drain.
Immediately toss with hot dressing, green onions and celery.
Garnish with radishes and parsley.