This 1976 CIA report titled Nuclear Proliferation and the Intelligence Community is worth your time. The report’s beginning describes some bureaucratic IC changes with respect to nuclear proliferation.
I cannot think of a 1974 proliferation-related event which would have incentivized these changes. The bulk of the document contains the recommendations of a report on proliferation intelligence prepared for the Deputy Secretary of Defense. The findings make for interesting reading, but I am not in a position to assess them. Also, if you really want an early reference to the IC and nuclear terrorism, here it is: