steering gearbox is a system to reduce the effort of direction on vehicles by employing an external energy source to help to turn the rollers.
It is said to him that the power-assisted steering rack was invented in the Twenties by Klara Gailis and George Jessup in Waltham, Massachusetts, the United States. However, the known patent earliest related to the power-assisted steering was classified (as recorded by the office of the patents of the USA) on August 30, 1932, by Francis W. Davis. There is another inventor credited with the invention of the power-assisted steering box by the name of Charles F. Hammond (American, carried with Detroit), who classified the similar patents, the first (as recorded by the Canadian office of intellectual property) on February 16, 1954 was classified.
Chrysler Corporation presented the first system available in the trade of power-assisted steering on the imperial Chrysler 1951 under the name of Hydraguide. The majority of the new vehicles have now the power-assisted steering, had with the tendencies towards the ordering of nose gear wheel, the greatest mass of vehicle and the broader tires, which all increase effort of necessary direction. It would be extremely difficult to operate the modern vehicles at low speeds (for example, while parking itself) without assistance.
The 605 box is a later design (starting late 70s I think) that is popular for replacing manual steering boxes on the 55-64 cars that would have had an external boost cylinder with factory PS. Its upside for those cars is that the output shaft has the same splines as the manual box, so you can keep your stock pitman arm. It offers no real incentive for replacing the 800 PS box used 65-up except maybe smaller size, and the spline size presents a swap problem in these years.