2000+ Exhaust on a '99? emission question

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?

Don't use the precats and keep the main cat. It does most of the work anyhow. The pcm wouldn't be happy as well as with the O2 sensors in the stock location both O2s will be seeing the same thing.

To use the O2 sensor locations on the manifolds you would need to convert to a 2000 PCM. Not easy and not worth it.

I wouldn't even use the 2000 manifolds. Just get an APN header.

As Talyn stated, run an aftermarket header. the 99 already has the "better" intake.

please don't put the pre cats on your jeep! I had to put louvers in my hood just so I could wheel my jeep without the pre cats baking the motor.

another + for an aftermarket header.

Just by a header, If you go with the 00-01 manifold I look forward to reading about clearance issues with the HP30