You may have to get an emissions test in which case you will more than likely fail.... Even though you only have reach the standards for that year of manufacture the old and tired cat, most likely different cat back, tired piston rings and tired fpr will most likely cause you to fail they're pretty strict..... In saying that I have heard that if you heat the cat up enough their efficency goes through the roof so in other words before it gets tested drive it like you stole it ..... Lol
Induction noise could be an issue too are you using the factory air box?