I would not make the profoundly stupid error of attempting to recruit name actors. I woudl get entirely unknown, mid 20's actors to play the actors. Youth has appeal, after all.
I would maybe involve one name actor to play the role of John Herbert Frid, the gifted man who made the show. It would have to be Matt Damon or Justin Timberlake as a young Jonathan Frid, though the latter obviously lacks Mr. Frid's acting abilities. Timberlake's ability to adlib and his capability to learn and adapt, however, would aide him in a successful portrayal of Frid, if it ever could come about. . It would be absolutely necesary to include the real Mr. Frid though, as an obviously mature Frid. He could play himself tirelessly promoting fan conventions in the 80's at least. In addition, it might be viable to consider uses the real Frid's voice for whatever actor plays him; after all, his cultured and sophisticated delivery helped raise his acting to the level of art at times. Few can match him in this respect. A deliberate imitation woudl be bound to fail as it would necessarily be derivative and third-rate because such brillant delivery is more of a reflection of Frid's own innate gifts rather than anything he learned at Yale or in his career; in other words, Frid cannot be taught.
I would touch on the stars' homosexuality. DS wasn't the Brady Bunch, and it would be painfully blah if some bigot attempted to whitewash the lives of the DS stars. A little campness, a little dark humor, and the homosexuality of a number of the male actors, if properly exploited, would be the only chance such a biopic would have at success (and a major success at that). Otherwise, obviously, it would be an MPI home video only release, which is terribly pathetic.
