The O Ring 7.7x2.3 is the cheapest item from this partsfiche.
In this schematic the "#seal,valve Stem" is used most often.
Parts such as the Gasket Kit A: O-ring,7.8x2.2, Gasket,cylin Head (mca), Gasket,cylin Head (nas), Gasket,ex.pipe (nas) are included in the Cb750sc Nighthawk 750 1983 (d) Usa Gasket Kit A parts fiche.