DEEP GROOVE smog pulley ID help please
 

Hi Gang, found this and don't see a stamped number, but it's got the "S" stamp and the look of definitely being a real & genuine GM pulley. Clearly deep groove. four bolt, 67 and earlier pulley? Original condition as shown also with likely original "A" head marked bolts. 5" diameter.

Anyone know what this is exactly?

Thanks in advance as always friends,
Anthony