We have seen some water migration issues when using the BMP blocks with the 4.500 bore and Cometic gaskets. Let me be clear. I like and use Cometic style gaskets all the time and I am a dealer for them. BUT in this specific case we use the Fel Pro with good success. Look at the water ports on the block. The water is migrating between the gasket layers. Water ends up in the crank case. Ot happened to us twice on different engines. Todd