What kind

If it has an aluminum main case, it's an overdrive. Chrysler made a cast iron case overdrive, but only one year in 1976. Easy to tell though. Stick it in high gear and turn the input shaft one revolution. If the output shaft turns more than one revolution, it's a overdrive. But if it's gotta aluminum main case, unless somebody swapped the gearset out, it's an overdrive, because all of them were from the factory that were aluminum.