If it passes the "motor test" as JimN outlines it should work on your A.
You'll need to wire in the regulator (square box in the photo) for the generator to work.
It does NOT get wired to the magneto kill switch. The generator/regulator combination work completely independent of the ignition switch. When the generator reaches it's cut-in RPM the regulator will automatically connect it to the battery, and disconnect it again when the generator slows down or stops spinning.
Note the OEM generator does NOT use a fan - there is nothing missing off the pulley.