That's good to know, Paul. I haven't opened the machines yet, so I don't know what stepper motors they have and whether I can use their drivers.
But what I found was that the first typewriter indeed had a stepper motor for the cylinder, too. It has a conical clutch thing, engaged by a solenoid. I'll probably glue the clutch and reuse the solenoid for something else. The vertical resolution of the revolving cylinder is about 70 steps per inch. Much smaller steps than I first measured.
But the horizontal steps of the typewheel carriage might be too large. Perhaps micro stepping can compensate.