So I found a local guy selling his MIlltek header for a great price, but the CAT doesn't function. I live in a state that only checks for CELs and I plan on tuning it out anyways. My question is, how hard is it to put a different CAT on the header? Is this something that a muffler shop should know how to do? Would it negate the header's additional performance gains (sawing off the old CAT and welding on a new one)? Thanks.

 

Cheapest thing to do might be use your old cat...weld it on...
Heck I know of a couple folks on a different board that have RMW "shorty" headers, with a stock can welded on...no cel, and 250 HP....

 

It's a 'measure, measure, cut, weld' affair. Any competent exhaust shop can do it.

Matching a cat shouldn't be difficult; just make sure you buy the correct diameter cat, and correct size & bolt pattern flange. You can probably use the stock cat, but there are cheap aftermarket cats out there for ~$100. Keep in mind though, aftermarket cats rarely last as long as OEM. GL.