The genesis of the 500 extended back to the 1963 model year, when Cadillac brought out a new, relatively lightweight 390 V8 to succeed the 1962 390 V8 that was based on Cadillac's first ohv V8 brought out in 1949. The 1963 engine displacement lasted just one year, with Cadillac bringing out a 429 ci. version for 1964, which was used through the 1967 model year. For 1968, Cadillac enlarged the displacement to 472 ci. IIRC, Cadillac began using a 500 ci. version of the engine in the Eldorado for 1970, with the RWD cars staying at 472 until 1973, when the 500 was available across the board. For the 1977 model year, coinciding with the debut of the smaller RWD deVille and Fleetwood models, the engine displacement was reduced to 425 ci. In 1980, the displacement was further reduced to 368 ci, and for 1981 this engine was the host of Cadillac's variable displacement system, known as V8-6-4, which was an idea just a little ahead of its time, and was dropped after 1981. IIRC, the engine soldiered on for a few more years in the Fleetwwod 75 line (limo) and died when Caddy began using the Oldsmobile 307 V8 in the RWD chassis.