No reason not to, unless your car is one of the 75-76es that are equipped with a catalytic converter. (Not all were, and not all that were originally equipped with them still have them.)
But the car should run fine on either, as long as you're not putting fuel in that has a lower octane rating than recommended.
--DD
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Pelican Parts 914 Tech Support
A few pics of my car:
http://www.pelicanparts.com/gallery/Dave_Darling