Well, most people like cheap performance additions. Instead of buying new headers, etc. from Coby or the like, a set of 20V 4AGE factory extractors can be modified to fit. By modify, all you need to do is drill two holes (the outer hole on each side of the flange). Use a 16V 4AGE exhaust gasket to get the new position of the end holes. The best ones to get are the blacktop extractors as these have a larger pipe diameter than the silvertop version. Simple!
However if you are keeping your stock exhaust, you will need to get some secondaries made up as the 20V manifold does not have a hole for the o2 sensor unlike the 16V one. On the 20v the sensor position is after the secondaries, instead of in the 4-2 section. This means the O2 sensor wires need to be extended.
Also keep in mind that the starter motor heat shield will need to be removed, unless you make a spacer between the head and manifold.