Drain pineapple, reserving 1/4 cup syrup.
Toss together pineapple and next 4 ingredients.
Line salad bowl with Bibb lettuce; spoon in salad mixture.
For dressing, stir reserved syrup into sour cream till well blended; chill.
To serve, spoon a little dressing atop salad.
Garnish with additional green grapes and Bibb lettuce, if desired.
Pass remaining dressing.