As has already been stated a couple of times, first, check the valve cover gaskets, second, check the intake gaskets. Don't fool around with the heads until you are absolutely sure that is the problem. Clean up the
oil with a rag and some solvent then run the engine a few minutes and observe where the
oil is coming from.
I had a small
oil leak at the lower rear corner of the valve cover gasket on the passenger side of my 351W. The bolts were not tight enough and the cover or the gasket had moved slightly. There was oil all over that head. I removed the cover, cleaned everything up, replaced the cover and gasket making sure that everything was aligned. No more problems.
Wayne