Well, Big Block Chevrolet's came with large rectangular ports on Hi perf applications and they also came with Oval ports for mild perf and everyday driver applications. There are numerous sizes of Oval port, earlier large design and later "peanut port" smaller sizes primarily desined for truck engines. It appears you have large rect port heads and a oval port manifold. You may also have, which it appears, aftermarket aluminum heads, that may take a specific intake. Not enough info supplied in the photos. That being said and while not ideal, A rect intake will fit and work on oval port heads, not the other way around. Note: there is also Tall deck blocks which have a taller deck, this maked the head seperation higher, thus wider, these require spacer plates or a specific tall deck intake. I don't think this is the case in your situation. I appears that you may only need a rect port intake.