As has been said if it is a Factory installation it would be a flight-o-matic. If it is a Factory installation it would be some different than a car trans. The truck trans used a vacuum/electric kickdown solenoid that protrudes at the drivers side rear of the transmission. All truck transmissions started in first gear and are a full three speed transmission.
If your truck is a conversion then you would have a manual kickdown lever to the trans.
Not all transmission guys today are fluent in these transmissions so if you do not rebuild it yoursel you will want to find someone who worked on these older transmissions. they will know them and make your experience more pleasent.
Here is an unashamed plug. If you do not rebuild it yourself and cannot find someone to do it for you write me.
All the parts are available for your transmission through Studebaker Venders, Especially Studebaker internationa.