Thank you for helping me build my case.
As it turns out, I was wrong. New York held the #1 spot throughout the 1960s. It was the 1970 census that pushed California to the #1 spot.
In the 1960 election, New York was #1 by a wide margin with 45 electoral votes. California was tied with Pennsylvania with 32 apiece. Both Illinois and Ohio had more votes than Texas. Believe it or not, Florida had only 10 electoral votes.
California closed the gap following the 1960 census trailing New York 43-40. Following the 1970 census California took over #1 by a 45-41 margin. Pennsylvania held the #3 spot with 27, one ahead of both Illinois and Texas at 26.