The 1938 and early 1939 Commander and President used a T88 transmission that laid sideways as Gary noted.That was done to lower the hump.The problem was that if you did not keep the oil level topped off the front bearing in the transmission would soon fail
and other lubrication problems caused Studebaker to return to the regular setup later in 1939. Graham also used the T88 for awhile.
You probably have to find a floor section from a later 1939 if you wanted to install a later transmission with a floor shifter. Some 1938 cars came with a dash mounted shifter and some 1939 cars came with column shifters, so it becomes confusing.
You can not simply add an overdrive section to a regular transmission.