We have the stock 318 cast iron exhaust manifolds that came with the car also. The car currently has headers on it. We are looking to find a set of 340 cast iron exhaust manifolds but wanted to see if they will bolt up first before we got them and found out they didn't fit or work. The car currently has a true dual exhaust and we are trying to keep it that way. The stock 318 ex. manfilds went to a y pipe and then to a single exhaust.