It was the draft of 1981 that brought the 49ers three of their four secondary standouts -- Ronnie Lott, Eric Wright, and Carlton Williamson, who teamed up with safety Dwight Hicks and terrorized QBs throughout the league. Walsh was SF GM at the time as well as head coach.
There is a caveat, though. Mark Haynes of the New York Giants (maybe the best pure cover cornerback I've ever seen, though he was a chronic malcontent who vanished after a few years) was selected that year, but he went down with an injury late in the year and Wright (I think) was named to replace him.