I am wanting to install the newer '00+ manifold design on my '99. I need a new manifold and want to redo most of the exhaust for higher clearance. I have found both Cat and Non-Cat down pipes but thought came into my mind, Would it possible to run just the Pre-Cats on a '99 and then remove the main Cat? Would there be computer errors? What kind of work would be needed to use the 2 upper o2 sensors? And the last question, would emissions be controlled enough through 2 Pre-Cats?