Do I have an E6 manifold?

Is an exhaust manifold called an E6 model when the long ford part # cast into it begins with E6? I have two manifolds that are cast with the long part # and they both begin with E6 however cast onto cylinder # 4 is the number 88 while on the other manifold is cast the number 87. Does that mean anything? Are these the sought after E6 manifold? Thanks