Grabbing the air from the fender area was needed due to the catalytic converter.
Consistent warm up control was desired and attempted with THERMAC, stove pipes from the exhaust Manifolds and other smog junk during the tune for emissions era starting about 1971 during the corporate run up to the Catalyst era.
Converter technology was technically ready at GM in 1971 however Lead had to be phased out of fuel first since lead is a converter bed poison so the government set unleaded fuel as a phase in for 1974 which cleared the way for the converter in 1975.
With the converter actually installed in 1975 reliable warm up became the key to maintaining the efficiency gain that the converter provided so that is why we see the funny ducting from the fenders to the carbs in that era.
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