Complex sentence: Reamy was also the department head of the convention's ambitious film program department that developed another first: a comprehensive, 80-hour, "all 35mm" science fiction film retrospective within a World Science Fiction Convention.
Split into simpler sentences: Reamy was also the department head of the convention's ambitious film program department. For the first time ever, he oversaw the development of a comprehensive, 80-hour, "all 35mm" science fiction film retrospective for a World Science Fiction Convention.