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1974 455 Hurst/Olds got a dual snorkel air cleaner with big dimple at the back for HEI distributor clearance. 1974 350 appearance package cars got the standard single snout piece with the big end bell for a flexible cold air hose. There is some difference in 350 aircleaners depending on if car has points or HEI distributor.
The 1975 aircleaner for both W30 and W25 should be same as the 1974 350 piece for an HEI car.
Which 1974 aircleaner have you found online? Is your 75 a W30 or a W25?
HEI became standard equipment for 1975 model year so it should have it. You could get the 75 with either 455 (W30) or 350 (W25). Both were 4-barrel with single catalytic converter exhaust.
So the 1974 wouldn't work? I haven't seen a 1975 air cleaner anywhere of late but have only looked for a week. The Search will begin in earnest shortly!