When I first took a look at the cover of Romancing the Past (Smithsonian Folkways), the beautiful new album from veteran Mexican trio Los Tres Reyes, the tux-clad, guitar-wielding musicians called to mind the strolling troubadours I’ve attempted to avoid in local Mexican restaurants. But once I dug into the album (elsewhere in the package, they’re pictured in less formal attire), the splendid, pitch-perfect performances made it clear these guys are no duffers.