All the 1959 Fords the team drive have 1964 Ford poverty hubcaps. Also during the series run, you can clearly see many post 1963 cars in the background.
John Santucci, who played mobster and safecracker Pauli Taglia, was, in his real past, a notorious jewel thief. The museum score depicted in the pilot episode was based on a real heist in which Santucci participated. In his previous career Santucci had been arrested by both Adamson and Farina.
Before becoming an actor, Dennis Farina was a member of the Chicago police department, as was series creator Chuck Adamson. The two were partners in Chicago's Central Investigative Unit, the real-life counterpart to the "Major Crimes Unit" in the series. In 2004, Farina joined the cast of Law & Order; his character transferred to the NYPD from Chicago.