I know we played both. But playing it and being "a zone team" are not the same thing. In the game I posted, UConn plays zone too. Nobody ever called them a zone team.
We stopped using man except for emergency situations prior to Lemoyne in 2009. I remember Flynn being quoted in preseason interviews that he tried to convince JB to play man the previous year. It was our primary defense during the 2003 NC run. JB played man against Lemoyne preseason 2009 to make a point.
The evolution from the man heavy teams of the 80's to the zone team we are now seemed to start during the '96 run and evolved until it really took hold in the early 2000's. If we were primarily a zone team in the '70's, I'll have to take your word for it. I grew up watching the '80's and early 90's teams.