On '91s (mine at least) the "Premium Unleaded Fuel Only" warning is printed on a plaque affixed to the instrument cluster bezel, located above the trip odometer between the speedometer and voltage gauge. At some point between '91 and '94 it changed to being printed directly on the lower right portion of the speedometer face.
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Russ
'91 black/black
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Russ
'91 black/black