My '75 SBC with HD cooling had the type of pulleys you are looking for. The water pump has a two groove pulley, and with HD cooling the PS belt goes over both the crankshaft and the water pump. When I look up the parts number for a PS belt there are two options, a short and a long belt. Both will work, but only the long one routes around the water pump.
I am running the long PS belt because it keeps the water pump running even if I break the alternator belt. I've had the alternator belt break once on the highway when I was running the short PS belt and it only took about five seconds for the water temp to get into the red once the water pump and fan stopped turning.