Factory Big Block Question

[1956cameo]

I had a question about the exhaust hangers for factory big block trucks. I have a 1969 factory short bed, 1/2 ton, big block truck, a 1970 factory long bed, 1/2 ton, big block truck, and two 1972 factory big block 3/4 ton suburbans. All of the trucks seem to be fairly original and complete. Both of the suburbans have the obvious big block hangers on them, but the two trucks dont seem to have the hangers (at the very least they dont have the large hangers on the rear section of the frame). Did the big block exhaust hangers come on all years of factory big block trucks? Were they the exact same for all years or were they different? Thanks for any input!