I have hear of the BB boys running even in to the 10's still using some type of factory cast manifold. But they make stroker kits for those motors too.
This is true but those guys have the manifolds extrude honed which costs as much as TTIs and they have mega mega dollars in those engines. If cost big money to look stock and go as fast as they do. Only the deep pocket guys can play that game.
The high hp engines with the cams designed to work with headers will really suffer when manifolds are used. Here are some dyno tests of some small block strokers with stock manifolds: