I purchased a 1973 Mach 1 with a non matching numbers to the power train. I have located the casting number behind the starter. D2AE-CA 4B24. from all the web sites I have understood its a 1972 Cleveland small block, High Output, Cobra Jet, Boss, date code 1974, February, 24th. My question is why does the main number indicate a 1972 yet the date code indicates 1974. Have I misunderstood how to properly decode? If any one could please explain I would appreciate it. Thanks.