Combine the whiskey, rum, lemon and pineapple in a punch bowl and let stand for at least 3 hours (overnight is best).
Dissolve the sugar in the water and stir into the whiskey mixture.
Refrigerate for at least an hour before serving.
To serve, slide the ice block into the bowl and grate about a quarter of a whole nutmeg over the top.
Ladle out 3-ounce servings into punch cups.
(This recipe makes about 24 servings).