vortec
Read somewhere that the vortec head is the best flowing factory cast iron head out of the box. Have people made 461's flow better? Yes, with alot of work. But, unmodified, Vortec flows best of all the factory cast iron heads. As far as the valves, it's the design of the head that will not allow it to respond to the smaller diameter stem. Much like overporting any head will decrease flow, same concept sorta. Like the article kinda said if you want to go over 400 HP with less than 400 cubes, you'll exceed the ability of the Vortec. Up to 400 HP, it's the best/cheapest way to go.