Oil drainback through the aluminum heads is usually a little slower than factory iron. But - the covers should seal it. Might want to check the cover flanges and replace the gaskets - make sure there is no oil residue left even from your fingers on theflanges or gasket, and don't use silicone on them either.
I used new rubber gaskets and bearing grease. I am getting an excessive amount of oil leakage on both sides of the motor at the sides above the last two plugs. It is basically running out. Not just seeping