This is a NOS AC GM catalytic converter shell for a 1981 and 1982 4.3 V8 engine.  I know the Pontiac cars had this engine and maybe the Oldsmobile and Buick but not sure.  This engine was used in the Pontiac cars including the Firebird, Grand Prix and Bonnevile.  It may fit other cars and other years but I am not sure.  Perfect condition in the original box.