Perhaps I’m lucky. My quite heavy duty vice has jaws that will clamp on the flywheel and still clear the sides of the crankcase enabling me to have both hands free for knocking up the cranks. You don’t need a big hammer for knocking up if the tapers are a good fit. You can check the quality of the fit by just pushing the cranks iinto the flywheel before assembly, you should be able to lift the flywheel by the crank without the flywheel dropping off. Keep your feet clear just in case!