Hello Mike. That machine sounds interesting, where do you pick this stuff up from, you have good contacts?
Generators are DC, alternators are AC.... although this classification has merged over the years.
Generators have no fixed operating speed as there is no AC frequency content to worry about.
They have a minimum speed where they become inefficient, maximum speed is usually limited by the commutator disintegrating, and increased inductance in the windings to increased rotation speed...... they generate less as speed increases over the sweet spot..
They are also inherently less efficient, the brushes span several commutator segments when switching from one armature winding to the next, significant current is wasted, these are called switching losses. This is why generators are bigger for a similar output to an alternator. An AC alternator uses diodes to do the switching, so there is no conduction overlap.
Thats why I never recommend generators, they are really too lossy with our limited horsepower, and the job can be done much better with AC and diodes.
Unless it has historic interest for a museum, practically it has little value for us off gridders.