The whole idea of the Ward Leonard drive is to accept line power at 60 Hz (25 or 50 Hz in some localities) and to generate: 1) dc at 120 volts for the spindle drive motor's shunt field, about 2 amps, and 2) dc at 240 volts for spindle drive motor's armature (and, obviously, the motor's series field), about 18 amps.
The 3-phase power input doesn't have to be perfect, but it should be within the motor's specifications, particularly the maximum current in the B-phase.
Since the 10EE starts with no load on the spindle, and hence little or no load on the dc generator, a static converter, used as a starter, with additional caps to supply a reasonably good B-phase for the three-phase motor, should work.
Use a clamp-type ammeter to ensure that the B-phase motor current is within limits when going from no spindle load to full spindle load.
Two-phase 10EEs are known to exist (mainly in Buffalo and Philadelphia), and these can more easily be converted to single-phase operation, as a single-phase motor is really a two-phase motor, anyway.
A tube drive 10EE needs very little B-phase power, and then only if it is equipped with a coolant pump (my 10EE was manufactured without a coolant pump).
For a tube drive 10EE with a coolant pump, a 1/2 HP three-phase motor is all that is needed for an idler as the coolant pump, which is the only three-phase load, is rated 1/4 HP.