Yes, the second plate is for metric threading, I purchased a metric set of gears from Miller Machine, who had made up a batch. Very handy when needed, just not needed enough now that I'm out of the MC business.
The Black Max is a fine motor, inverter rated, with a thermo switch which is wired to the VFD. Only once popped the thermo, too slow and too deep in direct will do that. On the 10EE you need to extend the motor shaft about an inch, and machine out the splines in the drive motor gear, cut a keyway in the drive gear, and make a plate which bolts all together. A bit of work but not difficult.
The drive is an Hitachi SJ200 which is a great unit, lots of parameters to tweak the unit. This EE has ELSR, and I added a switch which will double the reverse speed when rewinding for thread cutting. The sensorless encoding works really well, as you load the motor you can here the frequency boost to keep the rpm stable, great feature.