Digitized Congressional Hearings in the 1960s, 1970s, and 1980s

are freely available through the database at the University of New Orleans

To browse : http://louisdl.louislibraries.org/cdm4/browse.php?CISOROOT=/p120701coll25
To search: http://louisdl.louislibraries.org/cdm4/search.php?CISOROOT=/p120701coll25

The project is limited to those collection, U.S. Senate and House Hearings available to the University of Libraries. It may not be covered a whole congressional hearings collection published for that period.  But it offers another good access point for growing digitized older documents.