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I just spent the day looking locally for a 6" 1700rpm grinder with not much luck. Bill is right (not that I would argue with him) though You can buff with a 3450rpm motor. You just have to be a bit more careful with the heat and safety.
Junk washing machines are an excellent free source of 1750 rpm AC motors. (Usually the motor is still good and something else on the washer breaks.) You only need about a 1/4 to 1/2 hp motor for buffing, so don't look for grinder motors...