The overdrive trans is a different unit, you can find them relatively easily. You will need one from a '55 or later car or truck (either will work), those will use the original column shifter. You will need to make sure to fet one that has the same lever positons on the tranny as your original, the '55-'56 6 cylinder trucks are slightly different, but can be altered.
No 4 speed column shifts on Chevy trucks, exept for some early Corvair Greenbriars, and those don't interchange.
