A couple notes: RPO means Regular Production Option - as in you can order it from the factory with those parts. Also, in the 50s and 60s GM's market share boun

A couple notes: RPO means Regular Production Option - as in you can order it from the factory with those parts. Also, in the 50s and 60s GM's market share bounced between 40 and 50% (in fact 1986 was the first year that GM fell below 40% US market share). As such, competition was more fierce between GM divisions like Cadillac and Chevrolet than between GM and Ford per se. Thus the notes at the end comparing the Chevrolet engine to the Cadillac engine.