Bothl metal mating surfaces must be completely clean and polished to a very smooth condition to assure a perfect gasket seal between both surfaces. Did you happen to find the torque sequence and torque load imprinted on both exaust and cylinder head covers ?
Must retorque all mentioned bolts to their factory setting after first 5 to 10 run hours with a torquemeter as will have cede a bit due to heat which is quite normal.
Take advantage to clean all water paths to factory delivered condition for a spot on powerhed cooling, change thermo if rusted, salted, install new thermo gaskets as well.
Happy Boating
