Motor arrived today. It's the perfect size, weight, and ratings. It also includes a hall effect switch for monitoring RPMs which will be very useful because I will need to use that in order to select the right gear reduction ratios.
I will test it at 60 volts with the controller tomorrow.
This motor spins so smoothly I'm contemplating not bothering with a freewheel. If I do ditch the freewheel I have the option of later adding motor braking of some kind (regenerative or not).