Since the keyway is only there to align the flywheel to the crankshaft for ignition purposes no key is actually required to hold the flywheel in place. The flywheel will stay where it is seated on the tapered crankshaft if tightened down properly. When I advance timing I often leave the key out of the equation, when swapping coils, modules and wiring in chips the timing for spark is often in need of adjustments. Once the proper timing is found then that is where I often cut a new keyway in a flywheel. In your case all you need to align the flywheel to the crank is a center punch, mark the flywheel, mark on the crank stub.