Questions/Doubts Re: 1966 273 Commando Intake Manifold

While we're on the subject, does anyone know why the C.A.P. intakes are different? Other than the extra big boss added to the casting (as you can see in Mike's photo), what makes them different? By the way, that big threaded hole in the add-on doesn't go anywhere. It's just a blind hole with pipe threads (I think). I've seen people put plugs in them, but, there's no need since nothing passes through that hole.
The one on the lower right? Power brakes I believe.

intake resized.jpg