Right out of the gate, with 1966’s double-LP Freak Out!, Mothers of Invention proved to be one of the most audacious, inventive ensembles in rock music. (Frank Zappa’s name was not appended to the band’s until the early-‘70s.) Absolutely Free, the ‘67 followup, took the original concept a step further, ramping up the political/social commentary and satire of the debut on tracks like…