The Gen 1 is 1954 to 1985
the Gen 2 is the LT1 (1992 - 1996 with reverse water flow)
the Vortec is just a Gen 1 head with the Gen 2 combustion chamber
the Gen 3 is the LS's (1997 - 2007)
the Gen 4 is the LS's (2007-2013)
the Gen 5 is the LT's (2014 - )