Actress Lois Mitchell plays dual roles as both "Diana Sorrentino" and the hooker having sex with Harlan Ellison and Jane Allyson. Playing the latter character, Mitchell wears a wig and hides her face. This role isn't mentioned in the film's on-screen credits.
The post-Science Fiction Convention orgy (in which Harlan Ellison briefly appears straddled on a chair by Jane Allyson and Lois Mitchell), as well as several other scenes, were shot at Ellison's home which is recognizable for its funky decor and the voluminous number of books lining its walls. As with most of producer Harry H. Novak's films, the trailer largely consists of alternate shots, so if you watch it you can see an even longer shot of Harlan (although his face is obscured in that shot by his hair).
Produced to cash in on The Godfather (1972), but it was released a few months before that film.