On some engines, the factory cast exhaust manifold can be modified with having a second outlet added to it(welded), so it can be like a dual exhaust coming off of the cylinder head, as opposed to having to buy and install headers. If you look at a picture of some of the Fenton cast iron header manifolds, it would resemble that type of a setup. You would have the front 3 cylinders having a seperate manifold than the back 3 cylinders. Fabbing a set of tube headers might be easier than cutting and trying to section and weld a cast iron manifold. Just depends on what kind of stuff(equipment)you have access to.
