Kaala Patthar is one possibility, but looking at its amateur reviews on IMDb, I don't see the plot you describe. Shoot, because it sounds good anyway. It's 1979, with Amitabh Bachchan, Parveen Babi, (the busty) Neetu Singh, and Shashi Kapoor (and others) in it. M. is trying to do some google fu on your behalf; he's generally quite good at it.