When you installed the intake manifold did you cleanup all the old gasket etc/ While not disagrreeing with all thats been said I have found small blocks to love to draw oil in from the lifter valley. The gasket sets say never to use any sealer on the port sides. I ran into similar problem twice both times went and got the thickest intake gasket sets and used Indian head gasket shellac on the port sides. Went from oil smoke to zero. I have seen engines with broken rings not smoke that bad. Just my 10 cents