late 1965  first year ,early 1966 for the big block 396/375 one year only Z16 Malibu  Chevelle, Corvette 427/425, Impala, Biscayne ,396/375 ,427/425 big block proto type top adjuster alternator adjuster bracket with carb. spring bracket ,gm original , 396/375,427/425 ,this is a top alternator bracket that has been made this way from the factory  ,HAS NOT BEEN CUT OR MODIFIED, looks to be a prototype made for the 1966 year before they came out with the cookie cutter ones used from 66 to 68 big blocks for high performance cars with the carb. spring bracket ,RARE FIND ,I never seen one like it