Do I have to notch OEM valve covers to use them w/ Edelbrock performer 318/360

The stock steel valve covers shouldn't need any modification. The ones that usually have to be cut are the Cal Custom or Mopar performance cast aluminum valve covers. The cast aluminum covers are thicker in places that interfere with the aftermarket intake manifolds. I have an edelbrock manifold on my challenger with stock valve covers and had no issues at all. The Cal customs on my Duster on the other hand had to be modified slightly to clear the air-gap manifold on that one.