Hot off “Armageddon,” Bruce Willis is circling the MGM drama “Ump” as a possible next film, sources said.With Frank Oz directing, Willis would play the title character of a hitman who is called the Ump because he adheres to a strict set of rules. After rubbing out two of three triplet mob bosses, he ends up hiding out in New Jersey and cleans up that town while waiting for another chance to punch out the third mob boss. The project has caught the fancy of several A-list leading men. Willis is also mulling the Hollywood Pictures drama “Sixth Sense.” MGM brass hopes to get the film into production this year. Willis is repped by the William Morris Agency.