By O2 enhancers I think your talking about mil eliminators for the downstream sensors so you can streamline the exhaust flow though he the pre-cats. (On the exhaust manifolds.)
This is a great mod imo, and if your running a high flow cat you should have no problem passing a sniffer type emissions test. The manifolds are a pita to remove for cleaning, but the gains are well worth it. You may find some 'already been cleaned' manifolds in the classified section.
