Thanks guys.  This is a 55 series as the driveshaft is directly underneath the tractor.  As far as the serial number, I will look around the steering wheel.  One of my service manuals indicates that the number should be near the front of the engine but at issue here is that the paint is so thick on the cast iron that it makes it difficult to see if there is numbers there or not.  Hate to destroy all of the paint looking in the wrong place.   Thanks again for your help....Dave