"Big Block" is a generic term.
The standard alternator for L34 [350 hp] and L35 [325 hp] was the 1100834.
Optional 42 amp [K79] was 1100842; 61 amp [K85] 1100849.
All special high performance BBs [L78, L72, ZL1] used 1100837 37 amp with the deep-groove pulley.