[Mike Carr]

The HP penalty for a replacement head doesn't change the classification of a car; it is added after the fact. For example: A 1969 Camaro 427/425. You divide the shipping weight by the 425 to get the class; Class weight x 425 + 170. You add the 10 hp after. SO, in A/SA, you add 80 pounds (8 pound class, 10 hp penalty) after the fact.

The shipping weight never changes; it is what it is. If the shipping weight is 3,369 pounds, you will always use that number; divided by the HP (with OEM head) of the motor desired. You then add the hp penalty weight after. If a car falls into, say, GT/EA. 10 pound class. If an aftermarket head is permitted, with a 5 hp penalty, the aftermarket head version weighs 50 pounds more than a car with the same motor and an OEM head.

If I am wrong, someone can correct me, but I believe that is the way it works.