OK, reading through other posts has left me a little confused. My 96 with the 4.6. What is on this system that is stock? Two cats up front, one at the Y that goes back to the Mufflers or are those resonators?
stock is manifold to cat combined into a sigle third cat then single piping out to a y pipe and two mufflers.
Replacing the third cat can be done through an exhaust shop welding a y pipe in its place. I'd say your best bet would be to cut the third cat out and then take it to the place. They can't cut out any cats themselves because of epa bs.
the first two only convert two compounds, the thirds cat does three. I would suggest replacing the main cats with "three way" cats
This is the second time I've seen someone say that in the past 2 weeks or so. Where is this information coming from? The front 2 cats on my car were the only cats when I had my emissions test in CA, and I can tell you for sure that all three pollutants were cleaned up. I had virtually 0 on everything. This misinformation needs to stop spreading around.