This is for the LHS ONLY.. their is NO RHS matching design known commercially supplied or made or ever made or existing.. for the US passenger side.
This is for the mirror assembly only.. the fitting kit ie bracket, gasket etc.. are around $60.
1968 is also different a bit to 1969 Models.
This was a factory US option.
.jpg "Rocker Panel OUTER: 55-57 Chev (ea) - 4 dr")
.jpg "Valance Panel: 67 Firebird")