Even though I'm of blue-hair age now, Imma have to go. The last time I saw them live was when they played in the old Cow Barn (Animal Husbandry Building) in the 70's (I don't remember exactly which year) at MSU. It had the dirt floor and everything but they had a stage set up at the north end of the arena with chairs in the dirt and those 3 hombres filled that place up with sound. One of the best concerts I've ever been to.
Side note: I also took my wife-to-be to see a Ferrante & Teischer piano concert in the Cow Barn, too - probably the same year, give or take. Music Maker Productions used to have some pretty good first-level acts during that time.