Director Alan Parker's "Angel Heart" finally won an R rating Tuesday on what distributor Tri-Star Pictures said was its fourth try with the Motion Picture Assn. of America's rating board. Board chief Richard Heffner said in New York that Parker had made many cuts to gain the R rating, but Tri-Star insisted the cuts to the film were minor and that it would be released on schedule March 6. A studio spokesman said the "film is virtually unchanged" from the three versions that were given X ratings by the board. Most objectionable to the ratings board was, reportedly, a love scene between star Mickey Rourke and 19-year-old "Cosby Show" ingenue Lisa Bonet.