Regulatory timeline.
This doesn't cover the changes made by the refining and retail suppliers on their own due to other factors (wars in the middle east, profits, market demand, whatever)
Interesting the NY Times article about 1971 cars and fuels indicates a major shift in gasoline composition (and confusion) at the time. This is several years before GM helped the Feds deside cats were essential. Auto Makers and Oil Industry Get the Lead Out’ (Published 1970)
