First appearing in 1952 as a racecar, the evergreen Mercedes-Benz SL (mbusa.com) arrives for 2016 as an athletic GT with a folding metal top that retracts into the trunk. That feature isn’t new, but the front-end design is: It includes a steeply raked radiator grille inspired by the 300SL Panamericana racer of the 1950s, as well as a reshaped hood, bumper, and LED headlamps. Of the four variants, the two Mercedes-AMG models—the SL63 (shown, starting at about $151,000) and SL65 (starting at about $220,000)—deli…