That's probably a bracket for an AIR (air injection reactor) pump. There might also be a series of threaded holes in the exhaust manifold. Some California-specification engines came equipped with them. When the smog pumps were removed, most people either threaded the holes in the manifold for 1/4" pipe plugs or just folded the air tubes over and clamped or welded them shut.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!