Yes, they likely would... '67 chevys generally weren't designed to run e-85... Since that is dangerously close to leaded fuel! lol
Ethanol causes many of the rubber seals in the fuel system to swell, leak and/or split, as well as requiring re-tuning of the engine. If the entire fuel system is in good condition then the car could probably tolerate E10 reasonably well, although it would lead to seals and other parts perishing slightly faster. Also beware of Delrin-tipped carburettor needles, as these may be badly affected by ethanol. In general, keep as close as possible to the leaded petrol the car was designed for, which basically means high-octane unleaded with a squirt of upper cylinder lube/valve-saver.
ethanol is not good for any carb vehicle
E85 is VERY corrosive, you might as well fill your tank with acid and get it over with.
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