Id just have it sonic checked reguardless of the year. Mopars can be so random on some things that I wouldnt take any mopar book as the gospel. I bought a 318 (3.91 bore) that had been bored to 4.07 (.030 over 340). All the numbers on the block said 318 on it and it took a 318 drivers mount. Didnt have an x or anything else stamped on it out of the ordinary. I drove the motor about 2 months without any trouble. Ive been told so many things thhat this engine was but who knows?