The general manager of National Distributors has been named the South Portland company’s new president/ Tim Longstaff is succeeding Tim Kane, effective immediately, the company said Tuesday morning. Kane will remain a shareholder and advisor to the board of directors. National Distributors has more than 180 employees. It distributes beverages to retailers, mostly in southern Maine, with Anheuser-Busch its largest supplier. Longstaff has been with the family-owned company for more than 30 years, starting as a route salesman in 1984.