Correct, hence the open water ports at the front of the heads and the block off plates on the back of the heads. Without the correct water pump housing, I believe you would have to change the heads in order to use the block??

In researching information on this engine, I read the following......

"The water pump housing directs coolant straight from the radiator directly into the front of the heads. The heads have small sodium filled valves that can handle full throttle temperatures for long periods up long grades. The exhaust manifolds are unique to those heads."