The Incredible Two-Headed Transplant (1971)
Director: Anthony M. Lanza
Stars: Bruce Dern, Pat Priest, Casey Kasem, Albert Cole
Dr. Roger Girard is just trying to help his son. Unfortunately, he has some unorthodox ideas about how to help. Girard's research on head transplantation has been going pretty well, and he decides it's time to give his son, who has the mental capacity of an 8-year-old, another head.
Pops isn't picky, and opts to add the head of a psychotic killer to his son's body. Surprisingly, chaos ensues.