Does the cat have to be welded on?

[Jaxman]

A mechanic told me that a replacement cat for my 06 ls would have to be welded on but i'm finding conflicting information online. I see that direct fits don't appear to need welding and are simply bolted on. Is this true or does a cat always need welding? I am exploring the possibility of purchasing a wreck-pulled exhaust manifold with an attached cat but it appears they aren't that easy to find (thus far).

[Daox]

If you're just replacing the CAT then its going to need to be welded in. If you're replacing the whole section of pipe that contains the CAT then you can just bolt it in. That is if you can easily get it apart, the rust can be a huge pain. Maybe that isn't a problem in Florida.

[avguy]

... the rust can be a huge pain. ...

Ho yes. +1000 to that

And I suspect that lots of pros don't want to diddle with those rusted bolts and find it much easier (for them) to just hack it off and weld it back on.
But if you can get it unbolted from the mid pipe, and the mid pipe flange is in good shape then you're all set because the exhaust manifold connector won't be rusted.
If you can afford $207 + shipping, there's the #50445 cat from Rockauto that will bolt right in. They also have one for $168, but I usually try to go with what they recommend, unless the price is way up and over the rest. You might find a U-pull cat without rust in FL, but then you're dealing with however much raw gas was sent down into that cat by the previous owner(s).

[Jaxman]

I appreciate the responses. I had hopes that I could get my mechanic (retired, doesn't have welding equipment) to do it but i'm guessing i'll have to go the weld route. The car was purchased in FL but lived much of its life in upstate NY until I moved to FL in April. The rust has been pretty extensive and played a role in having to replace the entire front end recently.