Two words: Ernie Broglio. A few more: Long considered the standard for lopsided trades, Brock famously went to the Cardinals in a six-player trade three days before his 26th birthday, then 15 years later finished a Hall of Fame career that included 3,023 hits and the single-season and career records for stolen bases (both since broken by Rickey Henderson).
Broglio, the key player for the Cubs in deal, was a fine pitcher and former 20-game winner, who had been pitching since 1963 with an elbow injury he had kept hidden (going 7-19 with a 5.40 ERA over 2 1/2 seasons for the Cubs).