The Head says that the psychedelic view of heaven was designed by one of their newest arrivals, Timothy Leary. Dr. Leary, who died in 1996, was an advocate for psychedelic drugs, most notably LSD.
When the Head asks Marty where his harp is, he replies, "I left my harp in San Francisco." This is an allusion to Tony Bennett's signature song, "I Left My Heart in San Francisco."