Yes, the hull number is part of the HIN stamped on the transom. My hull number is PBJ000230280. PBJ is the builder code, 00023 is the hull number, and 80 is the year. Not sure but I think 02 is the month.
I agree that it's just a builder's part designation, I've seen them in other components on my boat. 30 is the length, beyond that it's hard to know. It looks like a 58 to me. Step #2? It was never intended for the owner, just to make sure the yard guys put the parts in the right place in the right boat.