Gas Question

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Do you know anything about the motor's history?
Generally, it's hard to bring compression up very much on these motors, so running 91, or even 89, octane should be ok. On the other hand, if someone rebuilt the motor using pop-up ppistons, or milled the heads a bunch, then compression could be higher.

For reference, c-code motors ran a dished piston with less than 9.0:1 compression (don't recall exact number) from the factory; a-codes ran a flat top and the revised compression ratio published by Ford was 9.2:1 (original data said 10:1, but that was later revised in a Ford tech bulletin). C-codes ran regular fuel and a-codes were premium-only motors.

As for your concern about the valves, if the motor has been rebuilt in the last 10, or even more, years it probably already has hardened valve seats and unleaded gas is not a problem. Actually, whether or not hardened seats are needed at all has been debated. I'm no expert and don't know the right answer. Maybe someone else can weigh in on that. Certainly, hardened seats allow you to sleep better at night.
It might be worth digging a bit - ask the previous owner for the owner before him and ask about the motor, etc. You might be able to track down the guy who last rebuilt the engine. How knows?

You can have a compression test done and figure out what kind of fuel is needed, but you would have to remove the heads to know about the valve seats. If the last guy was running non-leaded fuel, then I wouldn't worry much about it. After all, there are so many other things to worry about ....
Dont determine the engine you have by the Vin, get a Casting # and find out what you really have, My car's VIN said it had a C, the guy i bought it from said it was a rebuilt C....pulled the intake and had a 302 mexican (flat tops and thick main caps).........i would call the PO and see what has been done to the car...