[Johnny Mullet]

If the code was a (P0420) Cat efficiency below threshhold, then I bet my left nut the cat is bad. You can replace the cat, gut the cat, or bypass it, but legally, you need a new one.

If you chose to gut or bypass, then the rear O2 sensor needs not to go in. Leave it plugged in and tie it to the strut tower to keep the check engine light out.

Also, there is usually a reason the cat melted down, whether it's age or the car could have low compression or running rich. I would begin with a compression test on the cylinders before wasting money on a new cat to have it also melt down.