Referencing manuals instead of actual people who were alive and driving in the 1980s is a strategy that tells me you were either not there or too young to remember. I owned 1980s GM vehicles, I read the manuals (because there was no Internet in those days and life was boring in small town Oregon) and I distinctly remember there were references to Gasohol fuels in the manual. That does not mean actual pump regular unleaded contained ethanol. The pumps containing Gasohol were clearly labeled and you had to make a conscious decision to dispense it in your tank. I knew people who used it constantly and liked it, but most people were afraid of it.
When oil prices crashed in 1986, gasohol started disappearing and by the 90s I never saw it anymore.
In actual inflation adjusted terms, gasoline in 1979/1980 was the most expensive it had ever been, before or since. The idea of gasohol caught on because it was cheaper and also produced less smog, which was a BIG issue in those days for some cities. It was NOT used as an anti-knock additive, MTBE was widely used and the pumps were labeled as containing it.
