Super Stock Weight Breaks

Another question guys; How do I classify my car? I have a 1971 Ford Mustang, I am claiming it as a 2dr Fastback which is a lighter weight. If I choose to run the car in a traditional SS class the shipping weight for an 71 with the 280/305 engine at 10.65. When you do the math the car and driver shipping weight comes to 3418 lbs. If I claim the car as an 72 with 275/313 engine at 10.68 lbs the driver shipping weight comes to 3512 lbs. My question is If I want to run the car in SS/IA the weight break is 10.00-11.00 lbs. To run the car in this class what must the car weigh? Do I subtract 150 lbs from the shipping weight and this is the weight of the car or can I run the car at the bottom of the SS/IA weight break because the natural weight falls between the 10.00 to 11.00 weight? If someone has an clear answer on this please speak up, I called Glendora and of course they are on Holiday break so I couldn't get an answer there today.

Thanks guys!