These cars are sold individually. Trucks and couplers are not included. N Scale Kits' line of pewter kit cars was originally developed by Alan Curtis of AC models.
Here's what NSK has to say about them -
One of the earliest intermodal spine cars, these cars were loaded circus style, using specially adapted trailers, that ran on rollers on the axles along the high central spines. Large numbers of the cars were used by the Southern Pacific on their new intermodal service that started in 1959. Other railroads using the system and similar spine cars were the Erie, the KCS and the NH. With this kit, N Scale Kits have released an autocarrier that was used to transport cars across the SP system.