Talking of 70s movies, I watched The Conversation (1974) the other night.
Coppola said it was his favourite of all the movies he directed (which, considering his oeuvre is some statement) and supposedly Gene Hackman said it's one of his favourite acting performances.
Hackman plays a surveillance expert and is hired to follow and get information on a couple. It also stars Coppola favourites Robert Duvall, Harrison Ford, John Cazale and Frederic Forrest.