On the square drive nut, you run a tap drill for 5/16-24 through it and tap it all the way through from the old threaded side.

Then turn the nut around with a big washer behind the flats and a big hole in your prop. The prop is up against the flywheel that you shaved the fins from.

The nut and the prop hold the flywheel on.

On my flywheels, I took pliers and broke the fins off. Then I used a air powered die grinder to smooth everything over.

You can use a High Point balancer from B&B or a Dubro Balancer to balance the flywheel. If the flywheel has the key cast inside it, turn the arbor cone on the back side of the flywheel around and use the flat side against the flywheel.

Enjoy,

Jim