The only major make-up Jack Nicholson had to wear to become Jimmy Hoffa was fake nose and a set of false upper teeth (as seen in the behind-the-scenes footage on the DVD).
Jack Nicholson's daughter plays the young nun in the hospital scene where Billy Flynn is dying from his burns. According to Danny DeVito in the DVD audio commentary, Nicholson had asked him to give his daughter a small role. At first, Danny DeVito suggested she play the hooker in his hotel room in a later scene, drawing the trademark raised eyebrow from Nicholson. Since DeVito was joking he, of course, relented and cast her as a nun.
While promoting the movie on Live with Regis and Kathy Lee (1988), Danny DeVito said that Jimmy Hoffa, Jr. had visited the set one day and that when Jack Nicholson emerged from the make-up trailer made up as Hoffa himself, Jimmy, Jr. wept and said "That's my dad". At the time the movie was released, 1992, Jimmy, Jr. had not seen his father in seventeen years (Hoffa, Sr. disappeared in 1975).
At the time of this film's release, it had been seventeen years since Jimmy Hoffa disappeared, and ten years since he was declared "legally dead" (when authorities gave up actively searching for him).