There is a nice parallel part of the boss that coincides with the taper on the crankshaft. The biggest challenge is to hit the parallel part hard enough without raining blows on the pulley and wrecking it. I think I'd use an intermediate block of steel between the hammer and the boss, so that the hammer's contact surface is just above the pulley diameter. That will dull the blow a bit and make it harder to get it off, but it should protect the pulley. You need a really heavy anvil, a really heavy hammer, and good square hits on the boss. It might help to rotate the boss a bit every few hits. It would also help to have someone else hold the crankshaft (by the far end of course) to keep it exactly square to the anvil. Otherwise you'll need a really good support for the far end of the crankshaft. The key success factor is to get square, solid hits on the boss - anything that dulls the blow keeps the process from working.
