Perhaps the real question that needs answering here is what leads you to believe that 91 octane is not good enough for your Pantera?
Specifically, what observations have you made that have brought you to question fuel octane as being a problem for your Cleveland?
In general, a stock or even a mildly rebuilt Cleveland should be doing fine with 91 octane gasoline. What is the history and condition of your Cleveland? Has the engine received a recent tuneup and especially, has engine timing been confirmed?
Larry
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