Moore,
A 304 SS header for these cars is a waste of money. The reason I say this is because when Cobb made theirs they did a lot of testing and found the thermal (heat retention) values of the mild steel were superior to stainless. Even though stainless has this reputation for being more durable and prettier it's not the best performer. It will be easier for you to hit a lower price point with mild steel, which will also give better performance than an identical design out of 304 SS.