The 454 and 502 (Mark V) V8s with (any) Bravo drives have TWO water pumps. One is called the
raw water pump and the other is the
engine circulating pump. Both are belt driven and I think it doesn't matter if the engine has "closed cooling".

NB
PS: Unless I'm mistaken, the engine
circulating pump has a Rigid "metal" (cast iron..?) impeller and the
raw water pump has a Rubber impeller.