Personally I don't like the idea of turning down the flywheel or coring them. Reason being that unless you have a mandrel, which in this case would be a crankshaft with the mating taper you will have a very difficult time truing it. One way you could would be to core it then mount it on the crank of the assembled engine then mount the engine in a rotary table. You would need to indicate the crank in then move over and slowly turn the flywheel to true it with the crankshaft. Make sense? An easier way by far because you don't need as many setups is like I do in the attached photo. You make a prop hub and a timing ring, the timing ring is adjustable 360 degrees so the sensor can mount anywhere. Like anything in machining there are many ways to skin the cat. I tend to look for the simple way as well as the shortest way to the end. Hope this helps.