Nothing gigantic in the 1970s comes to mind, but there were certainly incidents which could be termed massacres and/or terrorist attacks.  Ma'alot, Israel in 1974; the Munich Olympics, '72; kidnappings and assasinations in Western Europe by various left-wing and right-wing groups.  The Kent State, Ohio shootings qualify in my opinion, as well as the Mexican government's machine-gunning student protesters.  But certainly nothing with mass deaths on the order of 9-11.

I have searched for something during the time periods that you requested that might compare to 9/11. I found very little during those years that might compare to the scale of events that occurred on 9/11/2001.  I have offered a few bits of information that might be helpful to you.  The most popular comparison between 9/11 is to Japan's attack on Pearl Harbor in 1941. "... five of eight battleships at Pearl Harbor were sunk or sinking, with the rest damaged. Several other ships and most Hawaii-based combat planes were also knocked out and over 2400 Americans were dead." (http://www.history.navy.mil/photos/events/wwii-pac/pearlhbr/pearlhbr.htm)

1941         Dec. 7,     Japan bombed Pearl Harbor.

1963        Nov 9, Twin disasters struck Japan as some 450 miners were killed in a coal-dust explosion, and 160 people died in a train crash.

1966        Mar 4, Canadian Pacific airliner exploded on landing in Tokyo and 64 died.

1966        Mar 5, 75 MPH air currents caused a BOAC 707 to crash into Mount Fuji and 124 died. (http://timelines.ws/countries/JAPAN_1941.HTML)

The Battle of Britain 10 July to 31 October 1940. 544 lost their lives during the period of the Battle.  A further 791 were killed in action or died in the course of their duties before the wars end. (http://www.raf.mod.uk/Bob1940/roll.html)