PINKHAM NOTCH, N.H. — Lynette Morrison-Norton, 58, a Jackson, N.H., grandmother raised in South Yarmouth, never imagined being a Mount Washington Auto Road stage driver. In her sixth year, she gives guided tours up the 7.6-mile sinuous road to the Northeast’s highest point by van and, when the road is closed to cars for the season, by specially-designed snowcoach through any whirlwinds of weather.