I'm familiar with the website that's selling Jerry Howell's plans (I bought some before), but never noticed until you pointed it out that the Tarot was one of his designs:
Designer and builder of model stirling, atmospheric
and gas engines and other model projects for which plans sets and/or casting kits are for sale.
That explains the mysterious hole in the base, it's for the faux ball governor. The Tarot has to be a 100% copy, minus a few extras.