anyone have aftermarket cats installed if so which ones and where did you get them i found some on summit but dont really know which ones to get i think its 2 inch inlets and outlets

Well you are not going to find any cat that fits on a stock Mark8's exhaust.The problem is on the drivers side the factory cats is part of the manifold.It IS possible to replace it with a cat with some custom work but it wont be easy.I would not want to try it.

What I and others have done is to "gut" the cats.
If you are interested do a search for "gutting cats".I did a little write up on it.

Why are you asking? Fixing a prob or looking for performance. . .

Why are you asking? Fixing a prob or looking for performance. . .fixing a problem

Well you are not going to find any cat that fits on a stock Mark8's exhaust.The problem is on the drivers side the factory cats is part of the manifold.It IS possible to replace it with a cat with some custom work but it wont be easy.I would not want to try it.

What I and others have done is to "gut" the cats.
If you are interested do a search for "gutting cats".I did a little write up on it. ok what if i gut the cats right and then where that 3rd one is put a real cat right there this is one that i am thinking of replacing it with http://store.summitracing.com/partdetail.asp?part=CTO-9513&N=120 4294923429 4294921547 300888

I'll be honest here, I dont know if it would work or not.I know a cat has to be fairly close to the engine to work correctly cause the gas has to be at least a certain temperature.
Sorry, I cant give an answer to this one.

I am running 3/4 headers and 2 cats on either side of the bell housing , originally I bought universal highflow cats which are round , when Kooks installed the exhaust they swapped the round for Oval shape high flow , a much better choice for appearance and ground clearence.... Where you are talking about putting the cat I put a dual in , dual out 2.5" Magnaflow "x" Muffler..I would think making a pipe for pass. side cat replace and gutting driverside , and adding a short pipe , would put the new cats in the same place as mine...Keep in mind O2 sensor flanges will need to be added to new pipes..