Rusted Nut, those blank knobs look like the ones in my '57 and I believe they are original, and they do match the other controls as you say.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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