Cats on longtubes...and evap
Where are you mounting your evap system (those that kept it)?
Thanks.
Also.. just putting them right behind the Headers will still not make them legal. What are your goals for using Cat's. ? You should really check your state or local SMOG laws if your trying to pass the test. (not saying that you will not pass or get checked if your setup is not compliant to the letter of the law, but technically, not legal).
What car are you working with and what state are you in?
For my EVAP on my Chevelle, I use the stock Chevelle venting system to the Chevelle Charcoal Canister. Did not use the Purge valve cause the PCM would not activated it anyway. It requires the fuel tank pressure and level sensor input into the PCM. So I setup up like the stock Chevelle setup with Vacuum to the Canister just to pull the flumes throught the Charcoal Canister.

I'll probably try to make the evap work also..
If you can get the EVAP system to work (with fuel tank inputs to the PCM) or just using the Charcoal Canister.. either way will be good.
But, you can pertty much get a good tuner to get it to run almost as clean as without the cats.
Keep us posted on what you do and the results.. as this subject is not really talked about much. I am considering doing a swap that will have to be Smog Compliant, so.. I'll be watching..
My last project I used Dynomax cats from summit. They look identical to Randoms at less than half the price. My tune is dead on 14.65:1 at low load and these Dynomax cats are garbage. THEY DON'T WORK. They also smell like a car with a gutted cat, might as well not have any. Spend the money and use Randoms.
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