An original 1951 3-sped transmission would have a shift-lever on the steering column.
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0702.htm

An original 1951 4-speed transmission would have shift lever in the middle of the floorboard.
http://chevy.oldcarmanualproject.com/1929_54chevyparts/04/221.HTM
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0714.htm