The stock cast iron manifold and factory head pipe makes a Tri-Y setup just like the thorly header, the only difference being the thorly would have smoother flow being mandrel bent pipe instead of a rough cast interior. Rockauto.com sells new cast manifolds for around the $140 mark. The fact that both are Tri-Y's may account for the fact that most people don't notice a difference when switching between them. Most foreign cars make more power per liter then the equivalent sized US made engine. It seems they aren't afraid to design in power building optimizations (such as Tri-Y exhausts) where US engines tend to just look at costs (a cast straight pipe with four flanges dumping to a single outlet and seemingly cast as thin as possible). Just a thought...