The 6 volt starter will be fine on 12, it doesn't run long enough to really make a difference (besides, it'll actually work better on 12!! ), I only mention it because of the flywheels. There is a difference in the tooth spacing between the 6 and 12 volt flywheels and the corresponding starter drives. As long as you use matching parts (6 volt starter with 216 flywheel or 12 volt starter ('55-'59 truck for stomper) and 235 flyhweel) you'll be just fine. Either way, you will want to use the 216 bellhousing and fron plate.
