Personally, I had no luck with the various whack-it approaches. If you have the time, search for a spanner wrench that claims to fit in the holes in the pulley (I think there are 3 holes, so the spanner would fit in 2 of them). I didn't want to wait, so I made one with a large steel carpenter square and a couple of bolts that fit in the pulley holes. That way you (or better, your assistant) can hold the pulley while you whack on the nut.
You will also need the Lisle tools in Post #2 to hold the flywheel when you take off (and later put back on) the harmonic balancer on the crank. Yes, you have to take it off to get at the hidden bolt on the water pump. Actually, I didn't use the flywheel lock to take off the crank bolt because my mighty HF air impact wrench took it right off. Others use a really big breaker bar with a pipe extension (and would have to use the flywheel lock).
2004.5 Silverado 3500 SRW 4x4, D/A (LLY), Ext. Cab, Long Bed
engineer837 aux rad, TxC CAI, LBZ MP, Scangauge II, Nicktane aux filter head, KD lift pump, 2008 PS pump, 2011 hydroboost, Frederico Swaybars, Rancho 9000XL, Torklift StableLoads, BFG AT/KO2, Lance 835 Camper often in the bed.