Clint Eastwood was given the choice of taking $25,000 in cash or $20,000 and a new Ferrari by Producer Dino De Laurentiis to play a small part in this movie. He chose the money and the Ferrari so his agent wouldn't be able to get ten percent of the car.
The Clint Eastwood incident was humorously referenced in Federico Fellini's segment of the anthology Histoires extraordinaires (1968). Terence Stamp played an actor arriving in Rome to do a movie, and as they leave the airport to go into the city, he suddenly sits up and asks where his Ferrari is. He was promised a Ferrari.
Clint Eastwood filmed his part after completing the final series of Rawhide (1959) and just before starting Le Bon, la Brute et le Truand (1966).
The film was never released outside of Europe, as United Artists bought the film when Clint Eastwood's career began to ascend. United Artists decided not to release it in theaters, but instead kept it in its library vault to prevent its viewing at Eastwood's request.