I decided to give up on the Venture wheels altogether, and just keep both tires and wheels for some other project down the line. I scored a 17″ Ninja 500 three-spoke rear wheel that matches the VTR wheel fairly closely. The wheel, including the cush drive and sprocket, was $38 shipped.
I also pivoted on the drivetrain. My podcast co-host is building a Harbor Freight Predator 212-powered KX:
It got me more interested in industrial motor + CVT bikes. I have on the way an an 6-1/2 horse LCT 208 snowblower engine, a 12V starter for it, and a generic Torq-A-Verter clone CVT.