domingo make sure it is not the cylinder head studs in the intake ports sucking oil up and through, also if the heads are ported do they have brass tubes for the push rod holes?sometimes those leak.

if those two parts are ok i would only use mr gasket intake gaskets, glue them to the cylinder heads and let the glue "set up", silicone the face of the gasket and the bottom of the intake ports, the silicone will allow the intake to slide down on the gasket as you tighten it down with out pulling the gasket with it.

is this a mp cross ram? or single 4 bbl? if it is a cross ram use lots of silicone down the bolt holes to keep them sealed as well.