the year splits for the model changes were
Advance Design 47-55
Task Force 55-59 (there were 2 versions of 1955's)
C/K first gen 60-66,
C/K second gen 67-72,
C/K third gen 73-87,
C/K fourth gen 88-99, etc.
Since our bodystyle went to 1991 on Blazers, Suburbans and Crew Cabs, you will see me list stuff as 73-87(91)...