There is an article in the Fall 2013 issue of the Fine Tool Journal about the Ellis wrench. The author, Dan Gaier, wrote an excellent piece about this wrench. He covered all the different variations, much as you two have done. He says that the wrench was made in 6, 8, 10, 12, and 18 inch sizes, but the only pictures posted are of the 6, 8, and 12 inch sizes. So while excellent information, it does not definitively answer the 10 inch question.
Unfortunately Dan did not post an email address.
Mike