Octane additives?

I used to know a guy who was a chemist for a refinery. He had a strongly built 65 Corvette and he would buy Toluene and Xylene from the paint store to mix with his gasoline to raise the octane so he didn't have to use race gas when he drove on the street. He claimed that those were the eight carbon compounds used to raise octane at the refinery. I would guess someone strong in chemistry could determine a mix ratio. The next question would be whether that would be economical these days or not.