Anyone know what 3" cat will fit our vehicles? Will this one do or can you recommend another one of theirs? http://www.car-sound.com/catalog/universal/530.aspx

Would it be OK to attach this via some pipe clamps to the vehicle? Just cut out the old one and clamp this one in, or should I have it welded (I'm looking for a semi-temporary solution). Mine is throwing codes and I thought I might as well get a 3" for whever I upgrade my downpipe in the future.

To install a 3 inch cat you'll either need adapters or replace the pipe. Sorry. For the money that you would have to spend you might as well get the high flow cat from the GP store that comes with the new DP.

Can't, their downpipe doesn't match the 3100 downpipe profile (I don't have a 3800, remember?). Plus, I've heard some nasty things about the high flow cats by R/T falling apart on the inside.

A couple of couplers to allow the cat to fit into place isn't a problem. I was just making sure it would fit (it apparently does) and I could clamp it in rather than welding.

i don't see why it wouldn't fit. it should have plenty of room to sit up in its spot. not sure with the 3.1's, but i know you can get one of those dummy o2 things if you want to get rid of the u-bend and not put a o2 sensor back in on a 3.8

I forget what the pipe size is but you can get a good universal high flow cat from summit for a descent price.