Charles Busch, Cheyenne Jackson, Martha Plimpton, Christopher Sieber, Tovah Feldshuh and Heidi Blickenstaff are lined up for the upcoming Actors Fund reading of the stage version of “Valley of the Dolls.”Blickenstaff (“[title of show]”) will play Neely, the up-and-coming thesp whose career is sidetracked by drugs in the lurid Hollywood tale. Busch portrays the legendary actress of a certain age who stars in a play with Neely, while Plimpton appears as a model-performer also tempted by pills. The script by Bob Hess and Doug Miller is based on the 1966 Jacqueline Susann novel, also the source material for the 1967 pic that starred Patty Duke. Carl Andress helms. One-night-only perf, a benefit for the Actors Fund, is set for March 15 at Gotham’s John Jay College.