The Blacktop has an inner form with the manifold in a more of the heart form in comparison to the Silvertop’s circular inlets (see “Throttles”). The Blacktop inlets at The pinnacle side can also be wider to allow for that larger inlet ports in the head. You should see “Throttles”, https://hectorypdow.bleepblogs.com/35082288/what-does-4age-20v-itb-mean