(Best) copper head gasket and offenhauser aluminum heads

[Lhead]

I have 53 merc flathead v8 with offenhauser aluminum heads. I ran into overheat]ing only on passenger side Sludge and and grit blocked at rear water jacket cavity. Checked gasket small hole in gasket does not line up with water jacket in rear of head. Very small hole in gasket is misaligned with cavity in head . Whats with the tiny holes inthe gasket . Seems highly restrictive to coolant flow. Thanks