One of the largest advertising accounts on the West Coast--the $70-million Paramount Pictures Corp. business--has been handed to the Los Angeles office of the ad firm D'Arcy Masius Benton & Bowles. The ad firm will primarily buy television, radio and print advertising time for the giant film company. D'Arcy is not expected to create advertising for Paramount, which like most film companies creates much of its own. The account had previously been handled by the Los Angeles office of the ad firm AC&R/DHB & Bess Advertising. D'Arcy will take over the account in May.