The environmental effects of lead in gasoline are extremely difficult to measure and have not been measured in real world settings. Theory suggests that there should be some bad effects, but it is very unclear if these should be called "major". There has been and still is some controversy about this.
Also lead was used in high performance military gasoline during WW2. I'm not sure if it might be even older than that. "1960s" is certainly too late for its introduction.
The form of lead used in gasoline is tetra-ethyl lead.
There are several lead substitutes used in modern lead-free gasoline:
[dimethyl sulfur]?: smells horrible. Slightly corrosive to engines. Not sure if it is dangerous. This was used in small quantities back to the 1930s. The amount used is now much higher in some countries where cheap high octane gasoline without lead is desired.
aromatic hydrocarbons (especially benzene, toluene, xylene?): Really seriously poisonous and carcinogenic. Much more dangerous than lead. Slightly corrosive to some engine parts. Civilised countries limit these by law to a very small percentage. These are present to some extent in crude oil, and small quantities have always been present in gasoline.
branched hydrocarbons: comparitively safe, but they add significantly to the cost, given the large quantities needed.
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