I have a 1961 - 235 that I need a water pump for. I was ask if it is a singal bypass or a dual bypass. What is the differance and does it matter.? Am I missing a adaptor plate of some kind? My block has a hole about 3" in diameter where the water pump bolts. I have a water pump that I thought was for this engine and it will not bolt up,it is the same as the water pump on my 216 engine. What do I need?

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