Kinda doubt that a 406 stroker with a 950 carb will have a PCV on it.
If you're using the chrome style breathers with the foam in them, try and blow through them with your mouth. Chances are they've filled with oil or condensation and are clogged.
Of course, you would think that it would blow out the dipstick tube first depending on whether the end of the tube is submerged or not.