Sounds like you are pulling oil from the cam valley into the bottom side of the intake to head, gasket area.. Very common when using modified parts.. If the intake to head angle is off a few degrees, which is more common than you would think, you will get mysterious oil usage. Pull the intake manifold and you will find the top edge of the intake gasket is crushed more than the bottom edge. Oil enters the lower side into the intake port and passes thru the combustion process un noticed..
Also aftermkt valve covers are famous for poor pcv function and oil use.