I need to see a schema from this set up if a neutral can be derived from this machine.

If the single phase load was balanced, or very small, eg to drive a relay coil or hour meter I can't see not too much of a problem to use the Earth connection.

If a larger 1Ø load has to be taken off, the starpoint from the motor generator output needs to be accessed, as done with normal generators.

The product of rotation, excitation and flux produces electricty.