To decide what voltage the starter is remove it and measure the diameter of the main shaft, 6 volt will be 14 millimeter diameter, 12 volt will be 12 millimeter. Then count the number of teeth on your flywheel to see which starter you need to use. With a 139 tooth flywheel you can use a 6 volt. If you have 168 teeth you most us a 12 volt starter. You can add a starter switch with a side terminal for a resister to use with a 12 volt system to a 6 volt starter if necessary My submitted, but not yet published, tech tip has a much easier method of determining 6v vs. 12v flywheel.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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