In 1972, the Brady Bunch ruled TV, the Eagles dominated radio, and Atari launched a video game revolution with Pong. But California pop culture was playing out a bit differently on two wheels, with candy-colored customs thundering down the boulevard, clearing away traffic and turning heads. It’s this era that Harley-Davidson distills in its new Seventy-Two, a laid-back Sportster with sparkling metal flake paint introduced Wednesday.