Are these sentences correct:
1-In the 1960's, he was a man revolutionizing modern music.
2-In the 1960's, he was one of the people revolutionizing modern music.
Additionally: Most style guides say not to use the ' with a decade. The 1960s, not the 1960's.
For me, #2 makes it clear there were many people doing this. #1 might suggest he was the only person doing so.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.