There's no such thing as an engine with no water pumps. Those engines have raw water pumps located on the lower left of the engine as you face the front of them belt driven. The cross overs (by-pass) are very common on performance big blocks. There's no need to double up on water pumps unless you're trying to control water flow for some reason. (automotive type pumps will slow flow). All that being said it might be good to have a marine mechanic check it out before you buy.