James, 49 Plymouth’s did not have overdrive. Your trans is either from a newer Plymouth, or a Chrysler, Desoto, or Dodge. Doesn’t matter which as they are interchangeable. What you need to know is what model overdrive it is. They are made by Borg- Warner. The number you need is cast in the transmission case. It is a number preceded by the letter r. Mine is from a 37 Chrysler and is a r6. It is a mechanical kick down model. If yours has a solenoid sticking out of it you may have a r10. Finding this number will pinpoint what unit you have and need parts for.