When it says "base only," you're only getting one side. Definitely not happy that this wasn't made clear in the description.
4x 9RPM motors plus 4x chuck assembly plus "base only" (which I incorrectly assumed meant two pieces) came out to just slightly more than the cost of the complete system, which made sense to me. With "base only" being just one side, the price difference is a bit ridiculous.
I'll look into fabricating something to go with the one side I received, but I'll end up returning it if fabrication isn't feasible.