It sounds like you have a prop hub for use on a magneto equipped engine. It just takes the place of the nut that holds the magneto on. I have used these before. What you can do is take a hole saw, and carefully cut the center of the magneto out, as large as is practically possible. Then dress it round, preferably with a lathe. You can then use it to "adapt" your prop hub to the crank. Just place the magneto center you made onto the crankshaft, and then screw on your prop hub. If running Gas/Glow, that's all there is to it. If running electronic ignition, then drill either the center piece you made, or the prop hub itself for a magnet to trigger the sensor.

Of course, if you are going to run the magneto ignition, then you must use the mag flywheel. Some people cut off the fins to reduce weight and eliminate the power robbing drag of the impeller blades. Rebalance the flywheel afterwards if you do this.

AV8TOR