It is my understanding that the only thing that can be modified in the stock class on the exhaust side is the piping BACK from the cat (ie Cat-back exahusts) and that the exhaust has to exit near the stock location (ie no side exit pipes.) headers and such are not allowed in stock class. So the msds headers would be illegal regardless of what rule you go by (the mod or the emission)...
hope this helps
Matt
