I found the datasheet eventually, see pages 45 and 135 of the Kollmorgen Stepper Solutions Catalog. Here is a summary:
NEMA23, 2 stack, winding type A (looks like the windings can be used in series, parallel or unipolar configurations)
Detent torque 0.12Nm.
Unipolar configuration: Rated current 4.6A, 0.42 ohms, 0.80mH per phase, holding torque 1.39Nm with 2 phases on.
Parallel configuration: 6.4A, 0.21 ohms, 0.80mH, 1.39Nm.
Series configuration: 3.3A, 0.84ohms, 3.2mH, 0.98Nm.
So it has 4 independent windings. For maximum torque, you should pair the windings in series or in parallel and drive them using a dual H-bridge. However, you can also wire it as a unipolar stepper, which is easier (no H-bridges needed, just mosfets) but has reduced performance.