Combine raisins and rum in a small saucepan; bring to a boil. Remove from heat; cover and let stand at room temperature 1 hour. Drain raisins; discard rum. Finely chop raisins, and set aside.
Beat eggs in a medium bowl at high speed of an electric mixer 3 minutes or until thick and pale. Combine sugar and cornstarch; gradually add sugar mixture to beaten eggs, beating constantly.
Transfer mixture to a large saucepan; stir in skim milk. Cook over medium heat, stirring constantly, until mixture thickens and just begins to boil. Remove from heat, and let cool. Stir in evaporated milk, vanilla, and chopped raisins. Cover and chill thoroughly.
Pour mixture into freezer container of a 1-gallon hand-turned or electric freezer. Freeze according to manufacturer's instructions. Pack freezer with additional ice and rock salt, and let stand 1 hour before serving.