We've had
ARH 1-7/8" long tubes and their catted X-pipe on our car for nearly 2 years, passes emissions every time. No codes, no issues.
This 2011 GT makes 430 whp with this set of headers + catted X-pipe, with our own custom 3" exhaust from the cats back + Steeda cold air. Dyno tuned with an SCT by True Street in McKinney. Emissions legal.
We've done some one-off custom exhaust systems also, like on this Boss 302-S race car, above.