The HX was introduced in July 1976 and was basicly a cosmetic upgrade on the HJ, although one major reason for the release of the HX was the introduction of new anti pollution requrements, Australian Desgn Rule 27a, to lower exhaust emmissions.
The cosmetic changes included a grille treatment, bright colours - like Deauville Blue , Large GTS decals, colour keyed mirror and bumpers. Bonnet back out made it the most distinctive of all four door Monaros.