Are you sure your calipers read zero when closed? .552 and .558. Closer to 1/2 than to 5/8 but no cigar. I assume no markings on the starters to indicate voltage? You never did post the part number and vendor of the new starter.
I forgot if you said or not, why did you buy a new starter?
I guess if you can't figure out if the starters are 12V or 6V, you will need to buy a 6V from one of the trusted vendors and move forward. Your old starter will probably be required as a core. Contact those vendors and ask questions before ordering.
In the past when 12V systems began, they used to only mark a starter voltage if it was 12V. The old 6V tags had no voltage. But don't count on that.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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