You've put up a 3K Bigport manifold. Which has a corresponding 3K Bigport head.
Now, 3K-B is a twin downdraft carb motor. With a 3K-B manifold and again, corresponding 3K-B head.
Difference is the twin carbs (obviously) and the fact the head and manifold have an extra bolt and a water port. For the water jacket in the 3K-B manifold.
Edit: To my knowledge, there is no designation for a Bigport Head