DO NOT USE THAT FLYWHEEL!!!!
If it has broken fins you can imagine the kind of beating this flywheel endured. Even a small hit or a prying motion WILL develop cracks in the cast iron. These cracks are invisible to the naked eye, but they are there and they grow bigger every time you run the engine.
If you use that flywheel, even at a low rpm, it WILL eventually explode like a grenade. It can even happen at idle! Even starting the engine puts an enormous amount of stress on the flywheel during the first revolutions (0 to 1400 rpm in half a second!). And when it explodes it ain't a small explosion. It can rip your arm, leg or head right off.
So, for your own safety and for the safety of those around you, please cut that thing in half so no one can ever use it again and throw it in the trash can.
Again, I'm not kidding, a damaged flywheel can KILL when it goes boom. Be careful.