If the code cannot be found, then identification can also be made by looking at the case measurement from front to back, not including the bell housing or rear pump section.
FMX = 9 7/8" Case Length (1968-1981)
FMX units are very similar to a Small Case, but they are not the same.
FMX units do not have a rear pump, and the filler tube goes into
the case (not the oil pan).